Fix class option

Closes #104.

NEWS.md

@@ -79,6 +79,9 @@
 * `read_parquet()` now reads the `FLOAT16` logical type as a real (double)
   vector.
 
+* The `class` argument of `parquet_options()` and the `nanoparquet.class`
+  option now work again (#104).
+
 # nanoparquet 0.3.1
 
 * This version fixes a `write_parquet()` crash (#73).

R/read-parquet.R

@@ -71,6 +71,10 @@ post_process_read_result <- function(res, file, options, col_select) {
 		)
 	}
 
+	if (length(options[["class"]]) > 0) {
+		class(res) <- unique(c(options[["class"]], class(res)))
+	}
+
   res
 }
 

src/RParquetReader.cpp

@@ -2065,9 +2065,8 @@ void RParquetReader::create_df() {
   Rf_setAttrib(columns, R_RowNamesSymbol, rnms);
   UNPROTECT(1);
 
-  SEXP cls = PROTECT(Rf_allocVector(STRSXP, 2));
-  SET_STRING_ELT(cls, 0, Rf_mkCharCE("tbl", CE_UTF8));
-  SET_STRING_ELT(cls, 1, Rf_mkCharCE("data.frame", CE_UTF8));
+  SEXP cls = PROTECT(Rf_allocVector(STRSXP, 1));
+  SET_STRING_ELT(cls, 0, Rf_mkCharCE("data.frame", CE_UTF8));
   Rf_setAttrib(columns, R_ClassSymbol, cls);
   UNPROTECT(1);
 }

tests/testthat/test-read-parquet-5.R

@@ -51,3 +51,20 @@ test_that("read a subset, factor to test Arrow metadata", {
     df[, 14, drop = FALSE]
   )
 })
+
+test_that("class", {
+  withr::local_options(nanoparquet.class = NULL)
+  tmp <- tempfile(fileext = ".parquet")
+  on.exit(unlink(tmp), add = TRUE)
+  write_parquet(test_df(), tmp)
+  expect_equal(class(read_parquet(tmp)), c("tbl", "data.frame"))
+  expect_equal(
+    class(read_parquet(
+      tmp,
+      options = parquet_options(class = c("foo", "bar", "data.frame"))
+    )),
+    c("foo", "bar", "data.frame")
+  )
+  withr::local_options(nanoparquet.class = "foobar")
+  expect_equal(class(read_parquet(tmp)), c("foobar", "data.frame"))
+})