Chapter-11/11.6 Resampling and Frequency Conversion（重采样和频度转换）.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 11.6 Resampling and Frequency Conversion（重采样和频度转换）\n",
    "\n",
    "重采样（Resampling）指的是把时间序列的频度变为另一个频度的过程。把高频度的数据变为低频度叫做降采样（downsampling），把低频度变为高频度叫做增采样（upsampling）。并不是所有的重采样都会落入上面这几个类型，例如，把W-WED（weekly on Wednesday）变为W-FRI，既不属于降采样，也不属于增采样。\n",
    "\n",
    "pandas对象自带resampe方法，用于所有的频度变化。resample有一个和groupby类似的API；我们可以用resample来对数据进行分组，然后调用聚合函数（aggregation function）:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "import numpy as np\n",
    "import pandas as pd"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "rng = pd.date_range('2000-01-01', periods=100, freq='D')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "2000-01-01    0.141136\n",
       "2000-01-02    0.955511\n",
       "2000-01-03   -0.334537\n",
       "2000-01-04    0.927611\n",
       "2000-01-05    0.522567\n",
       "2000-01-06    0.843023\n",
       "2000-01-07    0.108661\n",
       "2000-01-08    0.805668\n",
       "2000-01-09   -0.470524\n",
       "2000-01-10    1.162150\n",
       "2000-01-11   -0.754087\n",
       "2000-01-12   -1.846421\n",
       "2000-01-13   -0.322607\n",
       "2000-01-14    0.769992\n",
       "2000-01-15   -0.596838\n",
       "2000-01-16    0.865629\n",
       "2000-01-17   -0.394363\n",
       "2000-01-18    1.050334\n",
       "2000-01-19    0.203739\n",
       "2000-01-20    0.112178\n",
       "2000-01-21   -1.858528\n",
       "2000-01-22    0.921361\n",
       "2000-01-23   -1.034003\n",
       "2000-01-24   -0.319369\n",
       "2000-01-25    0.626385\n",
       "2000-01-26    2.319831\n",
       "2000-01-27    0.640064\n",
       "2000-01-28    0.762187\n",
       "2000-01-29   -0.053246\n",
       "2000-01-30    0.500993\n",
       "                ...   \n",
       "2000-03-11   -1.036658\n",
       "2000-03-12    0.569500\n",
       "2000-03-13   -0.279623\n",
       "2000-03-14   -1.593708\n",
       "2000-03-15   -1.552634\n",
       "2000-03-16    0.983931\n",
       "2000-03-17    0.269289\n",
       "2000-03-18    0.870814\n",
       "2000-03-19    1.642178\n",
       "2000-03-20   -0.109097\n",
       "2000-03-21   -1.891613\n",
       "2000-03-22   -1.867747\n",
       "2000-03-23   -0.173888\n",
       "2000-03-24    0.879418\n",
       "2000-03-25    0.814583\n",
       "2000-03-26   -1.683395\n",
       "2000-03-27   -0.141228\n",
       "2000-03-28    0.392206\n",
       "2000-03-29   -1.288983\n",
       "2000-03-30    1.052897\n",
       "2000-03-31   -0.297663\n",
       "2000-04-01    1.050265\n",
       "2000-04-02   -0.072390\n",
       "2000-04-03    1.482098\n",
       "2000-04-04   -0.276297\n",
       "2000-04-05    0.686525\n",
       "2000-04-06    1.368484\n",
       "2000-04-07    0.294756\n",
       "2000-04-08    1.237246\n",
       "2000-04-09    1.372567\n",
       "Freq: D, dtype: float64"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ts = pd.Series(np.random.randn(len(rng)), index=rng)\n",
    "ts"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "2000-01-31   -0.207554\n",
       "2000-02-29    0.299003\n",
       "2000-03-31   -0.095402\n",
       "2000-04-30   -0.146846\n",
       "Freq: M, dtype: float64"
      ]
     },
     "execution_count": 10,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ts.resample('M').mean()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "2000-01    0.210165\n",
       "2000-02   -0.051811\n",
       "2000-03   -0.131131\n",
       "2000-04    0.793695\n",
       "Freq: M, dtype: float64"
      ]
     },
     "execution_count": 12,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ts.resample('M', kind='period').mean()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "resample是一个灵活且高效的方法，可以用于处理大量的时间序列。下面是一些相关的选项：\n",
    "\n",
    "![](http://oydgk2hgw.bkt.clouddn.com/pydata-book/nwc0s.png)\n",
    "\n",
    "# 1 Downsampling（降采样）\n",
    "\n",
    "把数据聚合为规律、低频度是一个很普通的时间序列任务。用于处理的数据不必是有固定频度的；我们想要设定的频度会定义箱界（bin edges），根据bin edges会把时间序列分割为多个片段，然后进行聚合。例如，转换为月度，比如'M'或'BM'，我们需要把数据以月为间隔进行切割。每一个间隔都是半开放的（half-open）；一个数据点只能属于一个间隔，所有间隔的合集，构成整个时间范围（time frame）。当使用resample去降采样数据的时候，有很多事情需要考虑：\n",
    "\n",
    "- 在每个间隔里，哪一边要闭合\n",
    "- 怎样对每一个聚合的bin贴标签，可以使用间隔的开始或结束\n",
    "\n",
    "为了演示一下，下面用一个一分钟的数据来举例："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "rng = pd.date_range('2000-01-01', periods=12, freq='T')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "2000-01-01 00:00:00     0\n",
       "2000-01-01 00:01:00     1\n",
       "2000-01-01 00:02:00     2\n",
       "2000-01-01 00:03:00     3\n",
       "2000-01-01 00:04:00     4\n",
       "2000-01-01 00:05:00     5\n",
       "2000-01-01 00:06:00     6\n",
       "2000-01-01 00:07:00     7\n",
       "2000-01-01 00:08:00     8\n",
       "2000-01-01 00:09:00     9\n",
       "2000-01-01 00:10:00    10\n",
       "2000-01-01 00:11:00    11\n",
       "Freq: T, dtype: int64"
      ]
     },
     "execution_count": 14,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ts = pd.Series(np.arange(12), index=rng)\n",
    "ts"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "假设我们想要按5分钟一个数据块来进行聚合，然后对每一个组计算总和："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "1999-12-31 23:55:00     0\n",
       "2000-01-01 00:00:00    15\n",
       "2000-01-01 00:05:00    40\n",
       "2000-01-01 00:10:00    11\n",
       "Freq: 5T, dtype: int64"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ts.resample('5min', closed='right').sum()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "我们传入的频度定义了每个bin的边界按5分钟递增。默认，bin的左边界是闭合的，所以`00:00`值是属于`00:00`到`00:05`间隔的。设定closed='right'，会让间隔的右边闭合："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "1999-12-31 23:55:00     0\n",
       "2000-01-01 00:00:00    15\n",
       "2000-01-01 00:05:00    40\n",
       "2000-01-01 00:10:00    11\n",
       "Freq: 5T, dtype: int64"
      ]
     },
     "execution_count": 16,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ts.resample('5min', closed='right').sum()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "默认，每一个bin的左边的时间戳，会被用来作为结果里时间序列的标签。通过设置label='right'，我们可以使用bin右边的时间戳来作为标签："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "2000-01-01 00:00:00     0\n",
       "2000-01-01 00:05:00    15\n",
       "2000-01-01 00:10:00    40\n",
       "2000-01-01 00:15:00    11\n",
       "Freq: 5T, dtype: int64"
      ]
     },
     "execution_count": 17,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ts.resample('5min', closed='right', label='right').sum()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "可以看下图方便理解：\n",
    "\n",
    "![](http://oydgk2hgw.bkt.clouddn.com/pydata-book/d770h.png)\n",
    "\n",
    "最后，我们可能想要对结果的索引进行位移，比如在右边界减少一秒。想要实现的话，传递一个字符串或日期偏移给loffset："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "1999-12-31 23:59:59     0\n",
       "2000-01-01 00:04:59    15\n",
       "2000-01-01 00:09:59    40\n",
       "2000-01-01 00:14:59    11\n",
       "Freq: 5T, dtype: int64"
      ]
     },
     "execution_count": 18,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ts.resample('5min', closed='right', \n",
    "            label='right', loffset='-1s').sum()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "我们也可以使用shift方法来实现上面loffset的效果。\n",
    "\n",
    "### Open-High-Low-Close (OHLC) resampling（股价图重取样）\n",
    "\n",
    ">  Open-High-Low-Close: 开盘-盘高-盘低-收盘图；股票图；股价图\n",
    "\n",
    "在经济界，一个比较流行的用法，是对时间序列进行聚合，计算每一个桶（bucket）里的四个值：first（open），last（close），maximum（high），minimal（low），即开盘-收盘-盘高-盘低，四个值。使用ohlc聚合函数可以得到这四个聚合结果："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>open</th>\n",
       "      <th>high</th>\n",
       "      <th>low</th>\n",
       "      <th>close</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>2000-01-01 00:00:00</th>\n",
       "      <td>0</td>\n",
       "      <td>4</td>\n",
       "      <td>0</td>\n",
       "      <td>4</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-01 00:05:00</th>\n",
       "      <td>5</td>\n",
       "      <td>9</td>\n",
       "      <td>5</td>\n",
       "      <td>9</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-01 00:10:00</th>\n",
       "      <td>10</td>\n",
       "      <td>11</td>\n",
       "      <td>10</td>\n",
       "      <td>11</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "                     open  high  low  close\n",
       "2000-01-01 00:00:00     0     4    0      4\n",
       "2000-01-01 00:05:00     5     9    5      9\n",
       "2000-01-01 00:10:00    10    11   10     11"
      ]
     },
     "execution_count": 19,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ts.resample('5min').ohlc()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 2 Upsampling and Interpolation（增采样和插值）\n",
    "\n",
    "把一个低频度转换为高频度，是不需要进行聚合的。下面是一个有周数据的DataFrame："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Colorado</th>\n",
       "      <th>Texas</th>\n",
       "      <th>New York</th>\n",
       "      <th>Ohio</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>2000-01-05</th>\n",
       "      <td>0.138355</td>\n",
       "      <td>1.881517</td>\n",
       "      <td>0.655367</td>\n",
       "      <td>1.496932</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-12</th>\n",
       "      <td>-1.125212</td>\n",
       "      <td>-0.824337</td>\n",
       "      <td>0.803721</td>\n",
       "      <td>-0.672660</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "            Colorado     Texas  New York      Ohio\n",
       "2000-01-05  0.138355  1.881517  0.655367  1.496932\n",
       "2000-01-12 -1.125212 -0.824337  0.803721 -0.672660"
      ]
     },
     "execution_count": 20,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "frame = pd.DataFrame(np.random.randn(2, 4),\n",
    "                     index=pd.date_range('1/1/2000', periods=2,\n",
    "                                         freq='W-WED'),\n",
    "                     columns=['Colorado', 'Texas', 'New York', 'Ohio'])\n",
    "frame"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "当我们对这个数据进行聚合的的时候，每个组只有一个值，以及gap（间隔）之间的缺失值。在不使用任何聚合函数的情况下，我们使用asfreq方法将其转换为高频度："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Colorado</th>\n",
       "      <th>Texas</th>\n",
       "      <th>New York</th>\n",
       "      <th>Ohio</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>2000-01-05</th>\n",
       "      <td>0.138355</td>\n",
       "      <td>1.881517</td>\n",
       "      <td>0.655367</td>\n",
       "      <td>1.496932</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-06</th>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-07</th>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-08</th>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-09</th>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-10</th>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-11</th>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-12</th>\n",
       "      <td>-1.125212</td>\n",
       "      <td>-0.824337</td>\n",
       "      <td>0.803721</td>\n",
       "      <td>-0.672660</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "            Colorado     Texas  New York      Ohio\n",
       "2000-01-05  0.138355  1.881517  0.655367  1.496932\n",
       "2000-01-06       NaN       NaN       NaN       NaN\n",
       "2000-01-07       NaN       NaN       NaN       NaN\n",
       "2000-01-08       NaN       NaN       NaN       NaN\n",
       "2000-01-09       NaN       NaN       NaN       NaN\n",
       "2000-01-10       NaN       NaN       NaN       NaN\n",
       "2000-01-11       NaN       NaN       NaN       NaN\n",
       "2000-01-12 -1.125212 -0.824337  0.803721 -0.672660"
      ]
     },
     "execution_count": 21,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df_daily = frame.resample('D').asfreq()\n",
    "df_daily"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "假设我们想要用每周的值来填写非周三的部分。这种方法叫做填充（filling）或插值（interpolation），可以使用fillna或reindex方法来实现重采样："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Colorado</th>\n",
       "      <th>Texas</th>\n",
       "      <th>New York</th>\n",
       "      <th>Ohio</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>2000-01-05</th>\n",
       "      <td>0.138355</td>\n",
       "      <td>1.881517</td>\n",
       "      <td>0.655367</td>\n",
       "      <td>1.496932</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-06</th>\n",
       "      <td>0.138355</td>\n",
       "      <td>1.881517</td>\n",
       "      <td>0.655367</td>\n",
       "      <td>1.496932</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-07</th>\n",
       "      <td>0.138355</td>\n",
       "      <td>1.881517</td>\n",
       "      <td>0.655367</td>\n",
       "      <td>1.496932</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-08</th>\n",
       "      <td>0.138355</td>\n",
       "      <td>1.881517</td>\n",
       "      <td>0.655367</td>\n",
       "      <td>1.496932</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-09</th>\n",
       "      <td>0.138355</td>\n",
       "      <td>1.881517</td>\n",
       "      <td>0.655367</td>\n",
       "      <td>1.496932</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-10</th>\n",
       "      <td>0.138355</td>\n",
       "      <td>1.881517</td>\n",
       "      <td>0.655367</td>\n",
       "      <td>1.496932</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-11</th>\n",
       "      <td>0.138355</td>\n",
       "      <td>1.881517</td>\n",
       "      <td>0.655367</td>\n",
       "      <td>1.496932</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-12</th>\n",
       "      <td>-1.125212</td>\n",
       "      <td>-0.824337</td>\n",
       "      <td>0.803721</td>\n",
       "      <td>-0.672660</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "            Colorado     Texas  New York      Ohio\n",
       "2000-01-05  0.138355  1.881517  0.655367  1.496932\n",
       "2000-01-06  0.138355  1.881517  0.655367  1.496932\n",
       "2000-01-07  0.138355  1.881517  0.655367  1.496932\n",
       "2000-01-08  0.138355  1.881517  0.655367  1.496932\n",
       "2000-01-09  0.138355  1.881517  0.655367  1.496932\n",
       "2000-01-10  0.138355  1.881517  0.655367  1.496932\n",
       "2000-01-11  0.138355  1.881517  0.655367  1.496932\n",
       "2000-01-12 -1.125212 -0.824337  0.803721 -0.672660"
      ]
     },
     "execution_count": 22,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "frame.resample('D').ffill()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "我们可以选择只对一部分的周期进行填写："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Colorado</th>\n",
       "      <th>Texas</th>\n",
       "      <th>New York</th>\n",
       "      <th>Ohio</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>2000-01-05</th>\n",
       "      <td>0.138355</td>\n",
       "      <td>1.881517</td>\n",
       "      <td>0.655367</td>\n",
       "      <td>1.496932</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-06</th>\n",
       "      <td>0.138355</td>\n",
       "      <td>1.881517</td>\n",
       "      <td>0.655367</td>\n",
       "      <td>1.496932</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-07</th>\n",
       "      <td>0.138355</td>\n",
       "      <td>1.881517</td>\n",
       "      <td>0.655367</td>\n",
       "      <td>1.496932</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-08</th>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-09</th>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-10</th>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-11</th>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-12</th>\n",
       "      <td>-1.125212</td>\n",
       "      <td>-0.824337</td>\n",
       "      <td>0.803721</td>\n",
       "      <td>-0.672660</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "            Colorado     Texas  New York      Ohio\n",
       "2000-01-05  0.138355  1.881517  0.655367  1.496932\n",
       "2000-01-06  0.138355  1.881517  0.655367  1.496932\n",
       "2000-01-07  0.138355  1.881517  0.655367  1.496932\n",
       "2000-01-08       NaN       NaN       NaN       NaN\n",
       "2000-01-09       NaN       NaN       NaN       NaN\n",
       "2000-01-10       NaN       NaN       NaN       NaN\n",
       "2000-01-11       NaN       NaN       NaN       NaN\n",
       "2000-01-12 -1.125212 -0.824337  0.803721 -0.672660"
      ]
     },
     "execution_count": 23,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "frame.resample('D').ffill(limit=2)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "注意，新的日期索引不能与旧的有重叠："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Colorado</th>\n",
       "      <th>Texas</th>\n",
       "      <th>New York</th>\n",
       "      <th>Ohio</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>2000-01-06</th>\n",
       "      <td>0.138355</td>\n",
       "      <td>1.881517</td>\n",
       "      <td>0.655367</td>\n",
       "      <td>1.496932</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-01-13</th>\n",
       "      <td>-1.125212</td>\n",
       "      <td>-0.824337</td>\n",
       "      <td>0.803721</td>\n",
       "      <td>-0.672660</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "            Colorado     Texas  New York      Ohio\n",
       "2000-01-06  0.138355  1.881517  0.655367  1.496932\n",
       "2000-01-13 -1.125212 -0.824337  0.803721 -0.672660"
      ]
     },
     "execution_count": 25,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "frame.resample('W-THU').ffill()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 3 Resampling with Periods（对周期进行重采样）\n",
    "\n",
    "对周期的索引进行重采样的过程，与之前时间戳的方法相似："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Colorado</th>\n",
       "      <th>Texas</th>\n",
       "      <th>New York</th>\n",
       "      <th>Ohio</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>2000-01</th>\n",
       "      <td>1.451095</td>\n",
       "      <td>0.236027</td>\n",
       "      <td>-1.114785</td>\n",
       "      <td>1.245450</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-02</th>\n",
       "      <td>1.720449</td>\n",
       "      <td>-0.724853</td>\n",
       "      <td>-1.870676</td>\n",
       "      <td>1.089338</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-03</th>\n",
       "      <td>0.411774</td>\n",
       "      <td>-0.785979</td>\n",
       "      <td>1.749024</td>\n",
       "      <td>0.164739</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-04</th>\n",
       "      <td>-1.549051</td>\n",
       "      <td>-0.050722</td>\n",
       "      <td>0.002775</td>\n",
       "      <td>-1.606657</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000-05</th>\n",
       "      <td>1.011998</td>\n",
       "      <td>0.149377</td>\n",
       "      <td>-1.608262</td>\n",
       "      <td>0.992927</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "         Colorado     Texas  New York      Ohio\n",
       "2000-01  1.451095  0.236027 -1.114785  1.245450\n",
       "2000-02  1.720449 -0.724853 -1.870676  1.089338\n",
       "2000-03  0.411774 -0.785979  1.749024  0.164739\n",
       "2000-04 -1.549051 -0.050722  0.002775 -1.606657\n",
       "2000-05  1.011998  0.149377 -1.608262  0.992927"
      ]
     },
     "execution_count": 26,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "frame = pd.DataFrame(np.random.randn(24, 4),\n",
    "                     index=pd.period_range('1-2000', '12-2001',\n",
    "                                           freq='M'),\n",
    "                     columns=['Colorado', 'Texas', 'New York', 'Ohio'])\n",
    "frame[:5]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Colorado</th>\n",
       "      <th>Texas</th>\n",
       "      <th>New York</th>\n",
       "      <th>Ohio</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>2000</th>\n",
       "      <td>0.208662</td>\n",
       "      <td>-0.109971</td>\n",
       "      <td>-0.233464</td>\n",
       "      <td>0.138465</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2001</th>\n",
       "      <td>-0.401946</td>\n",
       "      <td>0.368050</td>\n",
       "      <td>-0.209196</td>\n",
       "      <td>-0.155851</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "      Colorado     Texas  New York      Ohio\n",
       "2000  0.208662 -0.109971 -0.233464  0.138465\n",
       "2001 -0.401946  0.368050 -0.209196 -0.155851"
      ]
     },
     "execution_count": 27,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "annual_frame = frame.resample('A-DEC').mean()\n",
    "annual_frame"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "增采样需要考虑的要多一些，比如在重采样前，选择哪一个时间跨度作为结束，就像asfreq方法那样。convertion参数默认是'start'，但也能用'end'："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Colorado</th>\n",
       "      <th>Texas</th>\n",
       "      <th>New York</th>\n",
       "      <th>Ohio</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>2000Q1</th>\n",
       "      <td>0.208662</td>\n",
       "      <td>-0.109971</td>\n",
       "      <td>-0.233464</td>\n",
       "      <td>0.138465</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000Q2</th>\n",
       "      <td>0.208662</td>\n",
       "      <td>-0.109971</td>\n",
       "      <td>-0.233464</td>\n",
       "      <td>0.138465</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000Q3</th>\n",
       "      <td>0.208662</td>\n",
       "      <td>-0.109971</td>\n",
       "      <td>-0.233464</td>\n",
       "      <td>0.138465</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2000Q4</th>\n",
       "      <td>0.208662</td>\n",
       "      <td>-0.109971</td>\n",
       "      <td>-0.233464</td>\n",
       "      <td>0.138465</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2001Q1</th>\n",
       "      <td>-0.401946</td>\n",
       "      <td>0.368050</td>\n",
       "      <td>-0.209196</td>\n",
       "      <td>-0.155851</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2001Q2</th>\n",
       "      <td>-0.401946</td>\n",
       "      <td>0.368050</td>\n",
       "      <td>-0.209196</td>\n",
       "      <td>-0.155851</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2001Q3</th>\n",
       "      <td>-0.401946</td>\n",
       "      <td>0.368050</td>\n",
       "      <td>-0.209196</td>\n",
       "      <td>-0.155851</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2001Q4</th>\n",
       "      <td>-0.401946</td>\n",
       "      <td>0.368050</td>\n",
       "      <td>-0.209196</td>\n",
       "      <td>-0.155851</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "        Colorado     Texas  New York      Ohio\n",
       "2000Q1  0.208662 -0.109971 -0.233464  0.138465\n",
       "2000Q2  0.208662 -0.109971 -0.233464  0.138465\n",
       "2000Q3  0.208662 -0.109971 -0.233464  0.138465\n",
       "2000Q4  0.208662 -0.109971 -0.233464  0.138465\n",
       "2001Q1 -0.401946  0.368050 -0.209196 -0.155851\n",
       "2001Q2 -0.401946  0.368050 -0.209196 -0.155851\n",
       "2001Q3 -0.401946  0.368050 -0.209196 -0.155851\n",
       "2001Q4 -0.401946  0.368050 -0.209196 -0.155851"
      ]
     },
     "execution_count": 28,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# Q-DEC: Quarterly, year ending in December\n",
    "annual_frame.resample('Q-DEC').ffill()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Colorado</th>\n",
       "      <th>Texas</th>\n",
       "      <th>New York</th>\n",
       "      <th>Ohio</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>2000Q4</th>\n",
       "      <td>0.208662</td>\n",
       "      <td>-0.109971</td>\n",
       "      <td>-0.233464</td>\n",
       "      <td>0.138465</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2001Q1</th>\n",
       "      <td>0.208662</td>\n",
       "      <td>-0.109971</td>\n",
       "      <td>-0.233464</td>\n",
       "      <td>0.138465</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2001Q2</th>\n",
       "      <td>0.208662</td>\n",
       "      <td>-0.109971</td>\n",
       "      <td>-0.233464</td>\n",
       "      <td>0.138465</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2001Q3</th>\n",
       "      <td>0.208662</td>\n",
       "      <td>-0.109971</td>\n",
       "      <td>-0.233464</td>\n",
       "      <td>0.138465</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2001Q4</th>\n",
       "      <td>-0.401946</td>\n",
       "      <td>0.368050</td>\n",
       "      <td>-0.209196</td>\n",
       "      <td>-0.155851</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "        Colorado     Texas  New York      Ohio\n",
       "2000Q4  0.208662 -0.109971 -0.233464  0.138465\n",
       "2001Q1  0.208662 -0.109971 -0.233464  0.138465\n",
       "2001Q2  0.208662 -0.109971 -0.233464  0.138465\n",
       "2001Q3  0.208662 -0.109971 -0.233464  0.138465\n",
       "2001Q4 -0.401946  0.368050 -0.209196 -0.155851"
      ]
     },
     "execution_count": 29,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "annual_frame.resample('Q-DEC', convention='end').ffill()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "增采样和降采样的规则更严格一些：\n",
    "\n",
    "- 降采样中，目标频度必须是原频度的子周期（subperiod）\n",
    "- 增采样中，目标频度必须是原频度的母周期（superperiod）\n",
    "\n",
    "如果不满足上面的规则，会报错。主要会影响到季度，年度，周度频度；例如，用Q-MAR定义的时间跨度只与A-MAR, A-JUN, A-SEP, A-DEC进行对齐（line up with）："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>Colorado</th>\n",
       "      <th>Texas</th>\n",
       "      <th>New York</th>\n",
       "      <th>Ohio</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>2000Q4</th>\n",
       "      <td>0.208662</td>\n",
       "      <td>-0.109971</td>\n",
       "      <td>-0.233464</td>\n",
       "      <td>0.138465</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2001Q1</th>\n",
       "      <td>0.208662</td>\n",
       "      <td>-0.109971</td>\n",
       "      <td>-0.233464</td>\n",
       "      <td>0.138465</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2001Q2</th>\n",
       "      <td>0.208662</td>\n",
       "      <td>-0.109971</td>\n",
       "      <td>-0.233464</td>\n",
       "      <td>0.138465</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2001Q3</th>\n",
       "      <td>0.208662</td>\n",
       "      <td>-0.109971</td>\n",
       "      <td>-0.233464</td>\n",
       "      <td>0.138465</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2001Q4</th>\n",
       "      <td>-0.401946</td>\n",
       "      <td>0.368050</td>\n",
       "      <td>-0.209196</td>\n",
       "      <td>-0.155851</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2002Q1</th>\n",
       "      <td>-0.401946</td>\n",
       "      <td>0.368050</td>\n",
       "      <td>-0.209196</td>\n",
       "      <td>-0.155851</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2002Q2</th>\n",
       "      <td>-0.401946</td>\n",
       "      <td>0.368050</td>\n",
       "      <td>-0.209196</td>\n",
       "      <td>-0.155851</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>2002Q3</th>\n",
       "      <td>-0.401946</td>\n",
       "      <td>0.368050</td>\n",
       "      <td>-0.209196</td>\n",
       "      <td>-0.155851</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "        Colorado     Texas  New York      Ohio\n",
       "2000Q4  0.208662 -0.109971 -0.233464  0.138465\n",
       "2001Q1  0.208662 -0.109971 -0.233464  0.138465\n",
       "2001Q2  0.208662 -0.109971 -0.233464  0.138465\n",
       "2001Q3  0.208662 -0.109971 -0.233464  0.138465\n",
       "2001Q4 -0.401946  0.368050 -0.209196 -0.155851\n",
       "2002Q1 -0.401946  0.368050 -0.209196 -0.155851\n",
       "2002Q2 -0.401946  0.368050 -0.209196 -0.155851\n",
       "2002Q3 -0.401946  0.368050 -0.209196 -0.155851"
      ]
     },
     "execution_count": 30,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "annual_frame.resample('Q-MAR').ffill()"
   ]
  }
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