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ARROW-5586: [R] convert Array of LIST type to R lists#4575

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ARROW-5586: [R] convert Array of LIST type to R lists #4575

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b63b705
+ class ListArray, ListArray$value_type
romainfrancois Jun 13, 2019
3557362
more methods for ListArray
romainfrancois Jun 13, 2019
375d3b5
ListArray to R list
romainfrancois Jun 14, 2019
5b62e28
+ListType::value_(field|type)
romainfrancois Jun 17, 2019
300f897
merge tests
romainfrancois Jun 18, 2019
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6 changes: 5 additions & 1 deletion r/R/List.R
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Expand Up@@ -18,7 +18,11 @@
#' @include R6.R

`arrow::ListType` <- R6Class("arrow::ListType",
inherit = `arrow::NestedType`
inherit = `arrow::NestedType`,
active = list(
value_field = function() shared_ptr(`arrow::Field`, ListType__value_field(self)),
value_type = function() `arrow::DataType`$dispatch(ListType__value_type(self))
)
)

#' @rdname DataType
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14 changes: 14 additions & 0 deletions r/R/array.R
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Expand Up@@ -118,12 +118,26 @@
)
)

`arrow::ListArray` <- R6Class("arrow::ListArray", inherit = `arrow::Array`,
public = list(
values = function() `arrow::Array`$dispatch(ListArray__values(self)),
value_length = function(i) ListArray__value_length(self, i),
value_offset = function(i) ListArray__value_offset(self, i),
raw_value_offsets = function() ListArray__raw_value_offsets(self)
),
active = list(
value_type = function() `arrow::DataType`$dispatch(ListArray__value_type(self))
)
)

`arrow::Array`$dispatch <- function(xp){
a <- shared_ptr(`arrow::Array`, xp)
if(a$type_id() == Type$DICTIONARY){
a <- shared_ptr(`arrow::DictionaryArray`, xp)
} else if (a$type_id() == Type$STRUCT) {
a <- shared_ptr(`arrow::StructArray`, xp)
} else if(a$type_id() == Type$LIST) {
a <- shared_ptr(`arrow::ListArray`, xp)
}
a
}
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28 changes: 28 additions & 0 deletions r/R/arrowExports.R
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31 changes: 31 additions & 0 deletions r/src/array.cpp
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Expand Up@@ -140,4 +140,35 @@ arrow::ArrayVector StructArray__Flatten(
return out;
}

// [[arrow::export]]
std::shared_ptr<arrow::DataType> ListArray__value_type(
const std::shared_ptr<arrow::ListArray>& array) {
return array->value_type();
}

// [[arrow::export]]
std::shared_ptr<arrow::Array> ListArray__values(
const std::shared_ptr<arrow::ListArray>& array) {
return array->values();
}

// [[arrow::export]]
int32_t ListArray__value_length(const std::shared_ptr<arrow::ListArray>& array,

@fsaintjacquesfsaintjacquesJun 17, 2019

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These are "low-level" functions, they don't perform any bound checking, you can segfault with the wrong i. Do they need to be exported?

@romainfrancoisromainfrancoisJun 17, 2019

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🤷‍♂ what's the rule about what is export worthy ?

int64_t i) {
return array->value_length(i);
}

// [[arrow::export]]
int32_t ListArray__value_offset(const std::shared_ptr<arrow::ListArray>& array,
int64_t i) {
return array->value_offset(i);
}

// [[arrow::export]]
Rcpp::IntegerVector ListArray__raw_value_offsets(
const std::shared_ptr<arrow::ListArray>& array) {
auto offsets = array->raw_value_offsets();
return Rcpp::IntegerVector(offsets, offsets + array->length());
}

#endif
45 changes: 45 additions & 0 deletions r/src/array__to_vector.cpp
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Expand Up@@ -547,6 +547,47 @@ class Converter_Decimal : public Converter {
}
};

class Converter_List : public Converter {
public:
explicit Converter_List(const ArrayVector& arrays) : Converter(arrays) {}

SEXP Allocate(R_xlen_t n) const { return Rcpp::List(no_init(n)); }

Status Ingest_all_nulls(SEXP data, R_xlen_t start, R_xlen_t n) const {
// nothing to do, list contain NULL by default
return Status::OK();
}

Status Ingest_some_nulls(SEXP data, const std::shared_ptr<arrow::Array>& array,
R_xlen_t start, R_xlen_t n) const {
using internal::checked_cast;
auto list_array = checked_cast<arrow::ListArray*>(array.get());
auto values_array = list_array->values();

auto ingest_one = [&](R_xlen_t i) {
auto slice =
values_array->Slice(list_array->value_offset(i), list_array->value_length(i));

@fsaintjacquesfsaintjacquesJun 14, 2019

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This is a relatively costly thing to do. I'm not sure how we can escape it. Do you keep a reference to the generated Slice/Array, or does it get consumed and transformed in something else. See #4366 (comment) for reference.

@romainfrancoisromainfrancoisJun 17, 2019

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::Allocate() makes an R list, and the various ::Ingest.*() fill that list.

I'll look if/how I can do this without actually calling Slice(), might be easy enough to just scan through values_array I guess.

@fsaintjacquesfsaintjacquesJun 17, 2019

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The challenging part is dealing with the bitmap and null_count.

@fsaintjacquesfsaintjacquesJun 17, 2019

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This can be a huge timesink, I think it's ok for now, but be wary that this will be a problem on large Array.

@romainfrancoisromainfrancoisJun 17, 2019

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I see. I don't think it's too much trouble to skip using Slice and use the bitmap of the values_array etc ... I'll have a look.

@romainfrancoisromainfrancoisJun 17, 2019

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🤔 yeah it's about the Array__as_vector(slice) which needs slice as a proper array already. The Converter api is designed to ingest all of an array, so I guess it would need some extra methods to only ingest a slice of an array without. I'll open another issue for that.

@romainfrancoisromainfrancoisJun 17, 2019

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https://issues.apache.org/jira/browse/ARROW-5628?filter=12344983

SET_VECTOR_ELT(data, i + start, Array__as_vector(slice));
};

if (array->null_count()) {
internal::BitmapReader bitmap_reader(array->null_bitmap()->data(), array->offset(),
n);

for (R_xlen_t i = 0; i < n; i++, bitmap_reader.Next()) {
if (bitmap_reader.IsSet()) ingest_one(i);
}

} else {
for (R_xlen_t i = 0; i < n; i++) {
ingest_one(i);
}
}

return Status::OK();
}
};

class Converter_Int64 : public Converter {
public:
explicit Converter_Int64(const ArrayVector& arrays) : Converter(arrays) {}
Expand DownExpand Up@@ -658,9 +699,13 @@ std::shared_ptr<Converter> Converter::Make(const ArrayVector& arrays) {
case Type::DECIMAL:
return std::make_shared<arrow::r::Converter_Decimal>(arrays);

// nested
case Type::STRUCT:
return std::make_shared<arrow::r::Converter_Struct>(arrays);

case Type::LIST:
return std::make_shared<arrow::r::Converter_List>(arrays);

default:
break;
}
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114 changes: 114 additions & 0 deletions r/src/arrowExports.cpp
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12 changes: 12 additions & 0 deletions r/src/datatype.cpp
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Expand Up@@ -281,4 +281,16 @@ int StructType__GetFieldIndex(const std::shared_ptr<arrow::StructType>& type,
return type->GetFieldIndex(name);
}

// [[arrow::export]]
std::shared_ptr<arrow::Field> ListType__value_field(
const std::shared_ptr<arrow::ListType>& type) {
return type->value_field();
}

// [[arrow::export]]
std::shared_ptr<arrow::DataType> ListType__value_type(
const std::shared_ptr<arrow::ListType>& type) {
return type->value_type();
}

#endif
2 changes: 2 additions & 0 deletions r/tests/testthat/test-DataType.R
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Expand Up@@ -297,6 +297,8 @@ test_that("list type works as expected", {
x$children(),
list(field("item", int32()))
)
expect_equal(x$value_type, int32())
expect_equal(x$value_field, field("item", int32()))
})

test_that("struct type works as expected", {
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