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Safely getting the column names of a CompressedSplitDFrameList #29

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LTLA opened this issue Dec 1, 2020 · 2 comments · Fixed by #31
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Safely getting the column names of a CompressedSplitDFrameList #29

LTLA opened this issue Dec 1, 2020 · 2 comments · Fixed by #31

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@LTLA
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LTLA commented Dec 1, 2020

Consider:

df <- DataFrame(X=1:26, Y=letters)
out <- split(df, rep(1:4, length.out=nrow(df)))
colnames(out)
## CharacterList of length 4
## [[1]] X Y
## [[2]] X Y
## [[3]] X Y
## [[4]] X Y

I just want a character vector of column names, so I might think of doing colnames(out)[[1]], but this fails for zero-length:

colnames(out[0])[[1]]
## NULL

The only safe way I can think of is:

colnames(unlist(out))
## [1] "X" "Y"

This is already somewhat unintuitive, but becomes a 3-liner if I want to change the column names:

df <- unlist(out)
colnames(df) <- c("x", "y")
out2 <- relist(df, out) # is metadata in 'out' retained in 'out2'?

So it would be nice to have a dedicated getter/setter for CSDFLs - following the columnMetadata example:

columnNames(out)
## [1] "X" "Y"
columnNames(out) <- c("x", "y")
@lawremi
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lawremi commented Dec 1, 2020

Good point. I get the mcols() vs. columnMetadata() distinction, but colnames() and columnNames() look like synonyms. Perhaps sharedColumnNames() instead? Feel free to submit a PR.

@LTLA LTLA mentioned this issue Dec 1, 2020
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@LTLA
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LTLA commented Dec 1, 2020

Poking around in the source code reveals an unexported commonColnames function in DataFrameList-class.R.

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Use commonColnames to get/set the column names of a DataFrameList. LTLA/IRanges
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@lawremi @LTLA