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Reindexing grouped data frames only update class if not grouped already #3438

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merged 3 commits into from
Mar 20, 2018
Merged

Reindexing grouped data frames only update class if not grouped already #3438

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3d99e83
only update class if not grouped already
krlmlr Mar 16, 2018
4306cc4
use Rf_inherits()
krlmlr Mar 20, 2018
b9b9c48
build_index_cpp() never touches class attribute
krlmlr Mar 20, 2018
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9 changes: 8 additions & 1 deletion src/group_indices.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -89,11 +89,18 @@ DataFrame build_index_cpp(DataFrame data) {
biggest_group = std::max(biggest_group, (int)chunk.size());
}

// The attributes are injected into data without duplicating it!
// The object is mutated, violating R's usual copy-on-write semantics.
// This is safe here, because the indices are an auxiliary data structure
// that is rebuilt as necessary. Updating the object in-place saves costly
// recomputations, but we need to be careful with the "class" attribute.
data.attr("indices") = indices;
data.attr("group_sizes") = group_sizes;
data.attr("biggest_group_size") = biggest_group;
data.attr("labels") = labels;
set_class(data, CharacterVector::create("grouped_df", "tbl_df", "tbl", "data.frame"));
if (r_match(CharacterVector("grouped_df"), get_class(data))[0] < 0) {
set_class(data, CharacterVector::create("grouped_df", "tbl_df", "tbl", "data.frame"));
}
return data;
}

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