ClickHouse/dbms/src/Functions/arraySlice.cpp

#include <Functions/IFunction.h>
#include <Functions/FunctionFactory.h>
#include <Functions/GatherUtils/GatherUtils.h>
#include <DataTypes/DataTypeArray.h>
#include <DataTypes/DataTypeNullable.h>
#include <Columns/ColumnArray.h>
#include <Columns/ColumnConst.h>
#include <Common/typeid_cast.h>
#include <IO/WriteHelpers.h>


namespace DB
{

namespace ErrorCodes
{
    extern const int LOGICAL_ERROR;
    extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
}

/** arraySlice(arr, offset, length) - make slice of array. Offsets and length may be < 0 or Null
  *   - if offset < 0, indexation from right element
  *   - if length < 0, length = len(array) - (positive_index(offset) - 1) + length
  *   indexation:
  *     [ 1,  2,  3,  4,  5,  6]
  *     [-6, -5, -4, -3, -2, -1]
  *   examples:
  *     arraySlice([1, 2, 3, 4, 5, 6], -4, 2) -> [3, 4]
  *     arraySlice([1, 2, 3, 4, 5, 6], 2, -1) -> [2, 3, 4, 5] (6 - (2 - 1) + (-1) = 4)
  *     arraySlice([1, 2, 3, 4, 5, 6], -5, -1) = arraySlice([1, 2, 3, 4, 5, 6], 2, -1) -> [2, 3, 4, 5]
  */
class FunctionArraySlice : public IFunction
{
public:
    static constexpr auto name = "arraySlice";
    static FunctionPtr create(const Context &) { return std::make_shared<FunctionArraySlice>(); }

    String getName() const override { return name; }

    bool isVariadic() const override { return true; }
    size_t getNumberOfArguments() const override { return 0; }

    DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
    {
        const size_t number_of_arguments = arguments.size();

        if (number_of_arguments < 2 || number_of_arguments > 3)
            throw Exception("Number of arguments for function " + getName() + " doesn't match: passed "
                            + toString(number_of_arguments) + ", should be 2 or 3",
                            ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);

        if (arguments[0]->onlyNull())
            return arguments[0];

        auto array_type = typeid_cast<const DataTypeArray *>(arguments[0].get());
        if (!array_type)
            throw Exception("First argument for function " + getName() + " must be an array but it has type "
                            + arguments[0]->getName() + ".", ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);

        for (size_t i = 1; i < number_of_arguments; ++i)
        {
            if (!isInteger(removeNullable(arguments[i])) && !arguments[i]->onlyNull())
                throw Exception(
                        "Argument " + toString(i) + " for function " + getName() + " must be integer but it has type "
                        + arguments[i]->getName() + ".", ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
        }

        return arguments[0];
    }

    void executeImpl(Block & block, const ColumnNumbers & arguments, size_t result, size_t input_rows_count) override
    {
        const auto & return_type = block.getByPosition(result).type;

        if (return_type->onlyNull())
        {
            block.getByPosition(result).column = return_type->createColumnConstWithDefaultValue(input_rows_count);
            return;
        }

        auto result_column = return_type->createColumn();

        auto & array_column = block.getByPosition(arguments[0]).column;
        const auto & offset_column = block.getByPosition(arguments[1]).column;
        const auto & length_column = arguments.size() > 2 ? block.getByPosition(arguments[2]).column : nullptr;

        std::unique_ptr<GatherUtils::IArraySource> source;

        size_t size = array_column->size();
        bool is_const = false;

        if (auto const_array_column = typeid_cast<const ColumnConst *>(array_column.get()))
        {
            is_const = true;
            array_column = const_array_column->getDataColumnPtr();
        }

        if (auto argument_column_array = typeid_cast<const ColumnArray *>(array_column.get()))
            source = GatherUtils::createArraySource(*argument_column_array, is_const, size);
        else
            throw Exception{"First arguments for function " + getName() + " must be array.", ErrorCodes::LOGICAL_ERROR};

        auto sink = GatherUtils::createArraySink(typeid_cast<ColumnArray &>(*result_column), size);

        if (offset_column->onlyNull())
        {
            if (!length_column || length_column->onlyNull())
            {
                block.getByPosition(result).column = array_column;
                return;
            }
            else if (length_column->isColumnConst())
                GatherUtils::sliceFromLeftConstantOffsetBounded(*source, *sink, 0, length_column->getInt(0));
            else
            {
                auto const_offset_column = ColumnConst::create(ColumnInt8::create(1, 1), size);
                GatherUtils::sliceDynamicOffsetBounded(*source, *sink, *const_offset_column, *length_column);
            }
        }
        else if (offset_column->isColumnConst())
        {
            ssize_t offset = offset_column->getUInt(0);

            if (!length_column || length_column->onlyNull())
            {
                if (offset > 0)
                    GatherUtils::sliceFromLeftConstantOffsetUnbounded(*source, *sink, static_cast<size_t>(offset - 1));
                else
                    GatherUtils::sliceFromRightConstantOffsetUnbounded(*source, *sink, static_cast<size_t>(-offset));
            }
            else if (length_column->isColumnConst())
            {
                ssize_t length = length_column->getInt(0);
                if (offset > 0)
                    GatherUtils::sliceFromLeftConstantOffsetBounded(*source, *sink, static_cast<size_t>(offset - 1), length);
                else
                    GatherUtils::sliceFromRightConstantOffsetBounded(*source, *sink, static_cast<size_t>(-offset), length);
            }
            else
                GatherUtils::sliceDynamicOffsetBounded(*source, *sink, *offset_column, *length_column);
        }
        else
        {
            if (!length_column || length_column->onlyNull())
                GatherUtils::sliceDynamicOffsetUnbounded(*source, *sink, *offset_column);
            else
                GatherUtils::sliceDynamicOffsetBounded(*source, *sink, *offset_column, *length_column);
        }

        block.getByPosition(result).column = std::move(result_column);
    }

    bool useDefaultImplementationForConstants() const override { return true; }
    bool useDefaultImplementationForNulls() const override { return false; }
};


void registerFunctionArraySlice(FunctionFactory & factory)
{
    factory.registerFunction<FunctionArraySlice>();
}


}