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#include <Functions/IFunction.h>
#include <Functions/FunctionFactory.h>
#include <Functions/FunctionHelpers.h>
#include <DataTypes/DataTypeArray.h>
#include <Columns/ColumnArray.h>
namespace DB
{
namespace ErrorCodes
{
extern const int ILLEGAL_TYPE_OF_ARGUMENT;
extern const int ILLEGAL_COLUMN;
}
/// arrayFlatten([[1, 2, 3], [4, 5]]) = [1, 2, 3, 4, 5] - flatten array.
class ArrayFlatten : public IFunction
{
public:
static constexpr auto name = "arrayFlatten";
static FunctionPtr create(ContextPtr) { return std::make_shared<ArrayFlatten>(); }
size_t getNumberOfArguments() const override { return 1; }
bool useDefaultImplementationForConstants() const override { return true; }
bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return true; }
DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
{
if (!isArray(arguments[0]))
throw Exception(ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT, "Illegal type {} of argument of function {}, expected Array",
arguments[0]->getName(), getName());
DataTypePtr nested_type = arguments[0];
while (isArray(nested_type))
nested_type = checkAndGetDataType<DataTypeArray>(nested_type.get())->getNestedType();
return std::make_shared<DataTypeArray>(nested_type);
}
ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t input_rows_count) const override
{
/** We create an array column with array elements as the most deep elements of nested arrays,
* and construct offsets by selecting elements of most deep offsets by values of ancestor offsets.
*
Example 1:
Source column: Array(Array(UInt8)):
Row 1: [[1, 2, 3], [4, 5]], Row 2: [[6], [7, 8]]
data: [1, 2, 3], [4, 5], [6], [7, 8]
offsets: 2, 4
data.data: 1 2 3 4 5 6 7 8
data.offsets: 3 5 6 8
Result column: Array(UInt8):
Row 1: [1, 2, 3, 4, 5], Row 2: [6, 7, 8]
data: 1 2 3 4 5 6 7 8
offsets: 5 8
Result offsets are selected from the most deep (data.offsets) by previous deep (offsets) (and values are decremented by one):
3 5 6 8
^ ^
Example 2:
Source column: Array(Array(Array(UInt8))):
Row 1: [[], [[1], [], [2, 3]]], Row 2: [[[4]]]
most deep data: 1 2 3 4
offsets1: 2 3
offsets2: 0 3 4
- ^ ^ - select by prev offsets
offsets3: 1 1 3 4
- ^ ^ - select by prev offsets
result offsets: 3, 4
result: Row 1: [1, 2, 3], Row2: [4]
*/
const ColumnArray * src_col = checkAndGetColumn<ColumnArray>(arguments[0].column.get());
if (!src_col)
throw Exception(ErrorCodes::ILLEGAL_COLUMN, "Illegal column {} in argument of function 'arrayFlatten'",
arguments[0].column->getName());
const IColumn::Offsets & src_offsets = src_col->getOffsets();
ColumnArray::ColumnOffsets::MutablePtr result_offsets_column;
const IColumn::Offsets * prev_offsets = &src_offsets;
const IColumn * prev_data = &src_col->getData();
while (const ColumnArray * next_col = checkAndGetColumn<ColumnArray>(prev_data))
{
if (!result_offsets_column)
result_offsets_column = ColumnArray::ColumnOffsets::create(input_rows_count);
IColumn::Offsets & result_offsets = result_offsets_column->getData();
const IColumn::Offsets * next_offsets = &next_col->getOffsets();
for (size_t i = 0; i < input_rows_count; ++i)
result_offsets[i] = (*next_offsets)[(*prev_offsets)[i] - 1]; /// -1 array subscript is Ok, see PaddedPODArray
prev_offsets = &result_offsets;
prev_data = &next_col->getData();
}
return ColumnArray::create(
prev_data->getPtr(),
result_offsets_column ? std::move(result_offsets_column) : src_col->getOffsetsPtr());
}
private:
String getName() const override
{
return name;
}
};
REGISTER_FUNCTION(ArrayFlatten)
{
factory.registerFunction<ArrayFlatten>();
factory.registerAlias("flatten", "arrayFlatten", FunctionFactory::CaseInsensitive);
}
}
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