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Casting generic binary to generic string #3607

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merged 3 commits into from
Jan 28, 2023
Merged

Casting generic binary to generic string #3607

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f37503a
Casting generic binary to generic string
viirya Jan 25, 2023
124205b
For CastOptions.safe as false case, applying optimized casting
viirya Jan 27, 2023
8c3c4f0
Remove offset
viirya Jan 27, 2023
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129 changes: 78 additions & 51 deletions arrow-cast/src/cast.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -156,8 +156,8 @@ pub fn can_cast_types(from_type: &DataType, to_type: &DataType) -> bool {

(Utf8, LargeUtf8) => true,
(LargeUtf8, Utf8) => true,
(Binary, LargeBinary) => true,
(LargeBinary, Binary) => true,
(Binary, LargeBinary | Utf8 | LargeUtf8) => true,
(LargeBinary, Binary | Utf8 | LargeUtf8) => true,
(Utf8,
Binary
| LargeBinary
Expand Down Expand Up @@ -185,7 +185,7 @@ pub fn can_cast_types(from_type: &DataType, to_type: &DataType) -> bool {
(Timestamp(_, _), Utf8) | (Timestamp(_, _), LargeUtf8) => true,
(Date32, Utf8) | (Date32, LargeUtf8) => true,
(Date64, Utf8) | (Date64, LargeUtf8) => true,
(_, Utf8 | LargeUtf8) => (DataType::is_numeric(from_type) && from_type != &Float16) || from_type == &Binary,
(_, Utf8 | LargeUtf8) => DataType::is_numeric(from_type) && from_type != &Float16,

// start numeric casts
(
Expand Down Expand Up @@ -1180,30 +1180,8 @@ pub fn cast_with_options(
}
Date32 => cast_date32_to_string::<i32>(array),
Date64 => cast_date64_to_string::<i32>(array),
Binary => {
let array = array.as_any().downcast_ref::<BinaryArray>().unwrap();
Ok(Arc::new(
array
.iter()
.map(|maybe_value| match maybe_value {
Some(value) => {
let result = std::str::from_utf8(value);
if cast_options.safe {
Ok(result.ok())
} else {
Some(result.map_err(|_| {
ArrowError::CastError(
"Cannot cast binary to string".to_string(),
)
}))
.transpose()
}
}
None => Ok(None),
})
.collect::<Result<StringArray, _>>()?,
))
}
Binary => cast_binary_to_generic_string::<i32, i32>(array, cast_options),
LargeBinary => cast_binary_to_generic_string::<i64, i32>(array, cast_options),
_ => Err(ArrowError::CastError(format!(
"Casting from {from_type:?} to {to_type:?} not supported",
))),
Expand Down Expand Up @@ -1236,30 +1214,8 @@ pub fn cast_with_options(
}
Date32 => cast_date32_to_string::<i64>(array),
Date64 => cast_date64_to_string::<i64>(array),
Binary => {
let array = array.as_any().downcast_ref::<BinaryArray>().unwrap();
Ok(Arc::new(
array
.iter()
.map(|maybe_value| match maybe_value {
Some(value) => {
let result = std::str::from_utf8(value);
if cast_options.safe {
Ok(result.ok())
} else {
Some(result.map_err(|_| {
ArrowError::CastError(
"Cannot cast binary to string".to_string(),
)
}))
.transpose()
}
}
None => Ok(None),
})
.collect::<Result<LargeStringArray, _>>()?,
))
}
Binary => cast_binary_to_generic_string::<i32, i64>(array, cast_options),
LargeBinary => cast_binary_to_generic_string::<i64, i64>(array, cast_options),
_ => Err(ArrowError::CastError(format!(
"Casting from {from_type:?} to {to_type:?} not supported",
))),
Expand Down Expand Up @@ -3436,6 +3392,77 @@ fn cast_list_inner<OffsetSize: OffsetSizeTrait>(
Ok(Arc::new(list) as ArrayRef)
}

/// Helper function to cast from `GenericBinaryArray` to `GenericStringArray`. This function performs
/// UTF8 validation during casting. For invalid UTF8 value, it could be Null or returning `Err` depending
/// `CastOptions`.
fn cast_binary_to_generic_string<I, O>(
array: &dyn Array,
cast_options: &CastOptions,
) -> Result<ArrayRef, ArrowError>
where
I: OffsetSizeTrait + ToPrimitive,
O: OffsetSizeTrait + NumCast,
{
let array = array
.as_any()
.downcast_ref::<GenericByteArray<GenericBinaryType<I>>>()
.unwrap();

if !cast_options.safe {
let offsets = array.value_offsets();
let values = array.value_data();

// We only need to validate that all values are valid UTF-8
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It seems a shame to duplicate this logic, but I guess it is hard to avoid whilst having this type signature

let validated = std::str::from_utf8(values)
.map_err(|_| ArrowError::CastError("Invalid UTF-8 sequence".to_string()))?;

let mut offset_builder = BufferBuilder::<O>::new(offsets.len());
offsets
.iter()
.try_for_each::<_, Result<_, ArrowError>>(|offset| {
if !validated.is_char_boundary(offset.as_usize()) {
return Err(ArrowError::CastError(
"Invalid UTF-8 sequence".to_string(),
));
}

let offset = <O as NumCast>::from(*offset).ok_or_else(|| {
ArrowError::ComputeError(format!(
"{}Binary array too large to cast to {}String array",
I::PREFIX,
O::PREFIX
))
})?;
offset_builder.append(offset);
Ok(())
})?;

let offset_buffer = offset_builder.finish();

let builder = ArrayData::builder(GenericStringArray::<O>::DATA_TYPE)
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.len(array.len())
.add_buffer(offset_buffer)
.add_buffer(array.data().buffers()[1].clone())
.null_count(array.null_count())
.null_bit_buffer(array.data().null_buffer().cloned());

// SAFETY:
// Validated UTF-8 above
Ok(Arc::new(GenericStringArray::<O>::from(unsafe {
builder.build_unchecked()
})))
} else {
Ok(Arc::new(
array
.iter()
.map(|maybe_value| {
maybe_value.and_then(|value| std::str::from_utf8(value).ok())
})
.collect::<GenericByteArray<GenericStringType<O>>>(),
))
}
}

/// Helper function to cast from one `ByteArrayType` to another and vice versa.
/// If the target one (e.g., `LargeUtf8`) is too large for the source array it will return an Error.
fn cast_byte_container<FROM, TO, N: ?Sized>(
Expand Down