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Merged
merged 2 commits into from
Sep 21, 2025
Merged

Support FixedSizeList for array_to_string #17666

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ab03ce2
Support FixedSizeList for array_to_string
Jefffrey Sep 19, 2025
1530f4b
Merge branch 'main' into array_to_string_fsl
Jefffrey Sep 20, 2025
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2 changes: 1 addition & 1 deletion datafusion/common/src/cast.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -313,7 +313,7 @@ pub fn as_fixed_size_list_array(array: &dyn Array) -> Result<&FixedSizeListArray
Ok(downcast_value!(array, FixedSizeListArray))
}

// Downcast Array to FixedSizeListArray
// Downcast Array to FixedSizeBinaryArray
pub fn as_fixed_size_binary_array(array: &dyn Array) -> Result<&FixedSizeBinaryArray> {
Ok(downcast_value!(array, FixedSizeBinaryArray))
}
Expand Down
100 changes: 52 additions & 48 deletions datafusion/functions-nested/src/string.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,8 @@ use arrow::array::{
};
use arrow::datatypes::{DataType, Field};

use datafusion_common::{not_impl_err, plan_err, DataFusionError, Result};
use datafusion_common::utils::ListCoercion;
use datafusion_common::{not_impl_err, DataFusionError, Result};

use std::any::Any;

Expand All @@ -39,12 +40,15 @@ use arrow::compute::cast;
use arrow::datatypes::DataType::{
Dictionary, FixedSizeList, LargeList, LargeUtf8, List, Null, Utf8, Utf8View,
};
use datafusion_common::cast::{as_large_list_array, as_list_array};
use datafusion_common::cast::{
as_fixed_size_list_array, as_large_list_array, as_list_array,
};
use datafusion_common::exec_err;
use datafusion_common::types::logical_string;
use datafusion_expr::{
Coercion, ColumnarValue, Documentation, ScalarUDFImpl, Signature, TypeSignature,
TypeSignatureClass, Volatility,
ArrayFunctionArgument, ArrayFunctionSignature, Coercion, ColumnarValue,
Documentation, ScalarUDFImpl, Signature, TypeSignature, TypeSignatureClass,
Volatility,
};
use datafusion_functions::downcast_arg;
use datafusion_macros::user_doc;
Expand Down Expand Up @@ -159,7 +163,26 @@ impl Default for ArrayToString {
impl ArrayToString {
pub fn new() -> Self {
Self {
signature: Signature::variadic_any(Volatility::Immutable),
signature: Signature::one_of(
vec![
TypeSignature::ArraySignature(ArrayFunctionSignature::Array {
arguments: vec![
ArrayFunctionArgument::Array,
ArrayFunctionArgument::String,
ArrayFunctionArgument::String,
],
array_coercion: Some(ListCoercion::FixedSizedListToList),
}),
TypeSignature::ArraySignature(ArrayFunctionSignature::Array {
arguments: vec![
ArrayFunctionArgument::Array,
ArrayFunctionArgument::String,
],
array_coercion: Some(ListCoercion::FixedSizedListToList),
}),
],
Volatility::Immutable,
),
aliases: vec![
String::from("list_to_string"),
String::from("array_join"),
Expand All @@ -182,13 +205,8 @@ impl ScalarUDFImpl for ArrayToString {
&self.signature
}

fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
Ok(match arg_types[0] {
List(_) | LargeList(_) | FixedSizeList(_, _) => Utf8,
_ => {
return plan_err!("The array_to_string function can only accept List/LargeList/FixedSizeList.");
}
})
fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> {
Ok(Utf8)
Comment on lines -185 to +209
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We don't need to guard here since type signature should enforce for us now

}

fn invoke_with_args(
Expand Down Expand Up @@ -282,16 +300,10 @@ impl ScalarUDFImpl for StringToArray {
}

fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
Ok(match arg_types[0] {
Utf8 | Utf8View | LargeUtf8 => {
List(Arc::new(Field::new_list_field(arg_types[0].clone(), true)))
}
_ => {
return plan_err!(
"The string_to_array function can only accept Utf8, Utf8View or LargeUtf8."
);
}
})
Ok(List(Arc::new(Field::new_list_field(
arg_types[0].clone(),
true,
))))
Comment on lines -285 to +306
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This is for string to array, but is similar to above in that type signature already ensures the arguments are string

}

fn invoke_with_args(
Expand Down Expand Up @@ -368,6 +380,20 @@ pub(super) fn array_to_string_inner(args: &[ArrayRef]) -> Result<ArrayRef> {

Ok(arg)
}
FixedSizeList(..) => {
let list_array = as_fixed_size_list_array(&arr)?;
for i in 0..list_array.len() {
compute_array_to_string(
arg,
list_array.value(i),
delimiter.clone(),
null_string.clone(),
with_null_string,
)?;
}

Ok(arg)
}
Comment on lines +383 to +396
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This is handling for when an element of the input list is a FixedSizeList itself

LargeList(..) => {
let list_array = as_large_list_array(&arr)?;
for i in 0..list_array.len() {
Expand Down Expand Up @@ -449,9 +475,8 @@ pub(super) fn array_to_string_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
Ok(StringArray::from(res))
}

let arr_type = arr.data_type();
let string_arr = match arr_type {
List(_) | FixedSizeList(_, _) => {
let string_arr = match arr.data_type() {
List(_) => {
let list_array = as_list_array(&arr)?;
generate_string_array::<i32>(
list_array,
Expand All @@ -469,29 +494,8 @@ pub(super) fn array_to_string_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
with_null_string,
)?
}
_ => {
let mut arg = String::from("");
let mut res: Vec<Option<String>> = Vec::new();
// delimiter length is 1
assert_eq!(delimiters.len(), 1);
let delimiter = delimiters[0].unwrap();
let s = compute_array_to_string(
&mut arg,
Arc::clone(arr),
delimiter.to_string(),
null_string,
with_null_string,
)?
.clone();

if !s.is_empty() {
let s = s.strip_suffix(delimiter).unwrap().to_string();
res.push(Some(s));
} else {
res.push(Some(s));
}
StringArray::from(res)
}
Comment on lines -472 to -494
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I removed this arm as the array (which is the first argument) must be a List type (List, Fixed or Large) by this point so this arm didn't make sense; even before my changes I don't think this arm was ever reachable as the return_type() function guarded arg[0] to be a list type 🤔

// Signature guards against this arm
_ => return exec_err!("array_to_string expects list as first argument"),
};

Ok(Arc::new(string_arr))
Expand Down
15 changes: 15 additions & 0 deletions datafusion/sqllogictest/test_files/array.slt
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Expand Up @@ -4703,6 +4703,11 @@ select array_to_string(arrow_cast(['h', 'e', 'l', 'l', 'o'], 'LargeList(Utf8)'),
----
h,e,l,l,o 1-2-3-4-5 1|2|3

query TTT
select array_to_string(arrow_cast(['h', 'e', 'l', 'l', 'o'], 'FixedSizeList(5, Utf8)'), ','), array_to_string(arrow_cast([1, 2, 3, 4, 5], 'FixedSizeList(5, Int64)'), '-'), array_to_string(arrow_cast([1.0, 2.0, 3.0], 'FixedSizeList(3, Float64)'), '|');
----
h,e,l,l,o 1-2-3-4-5 1|2|3

# array_to_string scalar function with nulls #2
query TTT
select array_to_string(make_array('h', NULL, NULL, NULL, 'o'), ',', '-'), array_to_string(make_array(NULL, 2, NULL, 4, 5), '-', 'nil'), array_to_string(make_array(1.0, NULL, 3.0), '|', '0');
Expand All @@ -4714,6 +4719,16 @@ select array_to_string(arrow_cast(make_array('h', NULL, NULL, NULL, 'o'), 'Large
----
h,-,-,-,o nil-2-nil-4-5 1|0|3

query TTT
select array_to_string(arrow_cast(make_array('h', NULL, NULL, NULL, 'o'), 'FixedSizeList(5, Utf8)'), ',', '-'), array_to_string(arrow_cast(make_array(NULL, 2, NULL, 4, 5), 'FixedSizeList(5, Int64)'), '-', 'nil'), array_to_string(arrow_cast(make_array(1.0, NULL, 3.0), 'FixedSizeList(3, Float64)'), '|', '0');
----
h,-,-,-,o nil-2-nil-4-5 1|0|3

query T
select array_to_string(arrow_cast([arrow_cast([NULL, 'a'], 'FixedSizeList(2, Utf8)'), NULL], 'FixedSizeList(2, FixedSizeList(2, Utf8))'), ',', '-');
----
-,a,-,-
Comment on lines +4727 to +4730
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This is interesting; it's formatting [[NULL, 'a'], NULL] to become this; note three - implying three nulls. I'm not sure if this is desired or if it should instead be -,a,- since the second element of the parent array is null (current code considers it to be two nulls, I guess because it represents a FixedSizeList(2)) 🤔

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I'll look into this as a follow-on issue

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Raised #17692


# array_to_string with columns #1

# For reference
Expand Down
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