Currently arrayCompact doesn't work with tuples like other array functions arraySort or arrayFilter.
Please consider adding such functionality to arrayCompact.
We need something like this... SELECT arrayCompact( (x,y) -> y, arr1, arr2) AS v

Current behavior:
`SELECT
    [('a', 1), ('a', 2), ('c', 3), ('a', 2)] AS arr,
    arrayCompact(x -> (x.1), arr) AS v,
    [('a', 1), ('c', 3), ('a', 2)] AS expected_v
`
![изображение](https://user-images.githubusercontent.com/33029350/93028896-5fca5e00-f617-11ea-9d55-e0a5d3c36697.png)


static bool needExpression() { return false; }
    static bool needOneArray() { return false; }
    static DataTypePtr getReturnType(const DataTypePtr & nested_type, const DataTypePtr &)
    {
        return std::make_shared<DataTypeArray>(nested_type);
    }
    template <typename T>
    static bool executeType(const ColumnPtr & mapped, const ColumnArray & array, ColumnPtr & res_ptr)
    {
        using ColVecType = ColumnVectorOrDecimal<T>;
        const ColVecType * src_values_column = checkAndGetColumn<ColVecType>(mapped.get());
        if (!src_values_column)
            return false;
        const IColumn::Offsets & src_offsets = array.getOffsets();
        const typename ColVecType::Container & src_values = src_values_column->getData();
        typename ColVecType::MutablePtr res_values_column;
        if constexpr (is_decimal<T>)
            res_values_column = ColVecType::create(src_values.size(), src_values_column->getScale());
        else
            res_values_column = ColVecType::create(src_values.size());
        typename ColVecType::Container & res_values = res_values_column->getData();
        size_t src_offsets_size = src_offsets.size();
        auto res_offsets_column = ColumnArray::ColumnOffsets::create(src_offsets_size);
        IColumn::Offsets & res_offsets = res_offsets_column->getData();
        size_t res_pos = 0;
        size_t src_pos = 0;
        for (size_t i = 0; i < src_offsets_size; ++i)