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GH-43349: [R] Fix altrep string columns from readr #43351

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Merged
jonkeane merged 6 commits into from
Jul 27, 2024
Merged

GH-43349: [R] Fix altrep string columns from readr #43351

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2a7eee6
check if altrep
jonkeane Jul 21, 2024
2a0da1e
ensure altrep strings aren't altrep first
jonkeane Jul 23, 2024
206e94d
a slightly different setup
jonkeane Jul 23, 2024
a22cb2e
more comment
jonkeane Jul 25, 2024
2a57460
An even simpler reprex
jonkeane Jul 27, 2024
990e2cf
ugh lintr
jonkeane Jul 27, 2024
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11 changes: 10 additions & 1 deletion r/src/arrow_cpp11.h
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Original file line number Diff line number Diff line change
Expand Up @@ -138,7 +138,13 @@ inline R_xlen_t r_string_size(SEXP s) {
} // namespace unsafe

inline SEXP utf8_strings(SEXP x) {
return cpp11::unwind_protect([x] {
return cpp11::unwind_protect([&] {
// ensure that x is not actually altrep first this also ensures that
// x is not altrep even after it is materialized
bool was_altrep = ALTREP(x);
if (was_altrep) {
x = PROTECT(Rf_duplicate(x));
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@nealrichardson nealrichardson Jul 24, 2024

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Add a comment about why we have to duplicate?

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@jonkeane jonkeane Jul 24, 2024

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Yeah, I'll expand what I have there

}
R_xlen_t n = XLENGTH(x);

// if `x` is an altrep of some sort, this will
Expand All @@ -152,6 +158,9 @@ inline SEXP utf8_strings(SEXP x) {
SET_STRING_ELT(x, i, Rf_mkCharCE(Rf_translateCharUTF8(s), CE_UTF8));
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@nealrichardson nealrichardson Jul 24, 2024

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Did we want to check whether Rf_translateCharUTF8() actually modified anything? Or do we trust that SET_STRING_ELT is a no-op in that case? I would imagine that in most cases, we already have ascii/utf-8 strings, so this whole function should be basically free. That should be easily verified by microbenchmarking.

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@jonkeane jonkeane Jul 24, 2024

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Something like this from above?

SEXP new_s = Rf_translateCharUTF8(s);
if (new_s == s) {
SET_STRING_ELT(x, i, Rf_mkCharCE(new_s, CE_UTF8));
}

Yeah, that's probably good. It'll also make this slightly more inline with what was there before (checking that not utf8)

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@jonkeane jonkeane Jul 25, 2024

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I've tried this, but after getting it to work with a bit of type faffing, doing the translate first we get errors with our utf string tests again.

}
}
if (was_altrep) {
UNPROTECT(1);
}
return x;
});
}
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17 changes: 17 additions & 0 deletions r/tests/testthat/test-csv.R
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Expand Up @@ -738,5 +738,22 @@ test_that("read_csv2_arrow correctly parses comma decimals", {
tf <- tempfile()
writeLines("x;y\n1,2;c", con = tf)
expect_equal(read_csv2_arrow(tf), tibble(x = 1.2, y = "c"))
})

test_that("altrep columns can roundtrip to table", {
tf <- tempfile()
on.exit(unlink(tf))
write.csv(tbl, tf, row.names = FALSE)

# read in, some columns will be altrep by default
new_df <- read_csv_arrow(tf)
expect_equal(tbl, as_tibble(arrow_table(new_df)))

# but also if we materialize the vector
# this could also be accomplished with printing
new_df <- read_csv_arrow(tf)
test_arrow_altrep_force_materialize(new_df$chr)

# we should still be able to turn this into a table
expect_equal(tbl, as_tibble(arrow_table(new_df)))
})