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Sorting

order_by

Sorts the range using a key selector function (key_selector) according to a direction (sort_dir).

key_selector must be a function that takes the range's elements as input and returns a value of an arbitrary type, i.e. \(f(x) \mapsto y\). The result value (of type y) is then used as the sorting key in the subsequent sorting algorithm.

sort_dir specifies whether the elements are sorted in ascending or descending order.

Comparison is done using operator< between elements of type y.

Signature
template <typename TKeySelector>
constexpr auto order_by( TKeySelector&& key_selector, sort_direction sort_dir ) const;
Example
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const auto words = std::vector{ "hello"s, "world"s, "here"s,
                                "are"s, "some"s, "sorted"s, "words"s };

const auto result = linq::from( &words )
                   .order_by( linq::size, linq::sort_direction::ascending )
                   .to_vector();

assert( result == std::vector{ "are"s, "here"s, "some"s,
                               "hello"s, "world"s, "words"s, "sorted"s } );

then_by

Sorts a range that was produced by order_by and serves to apply subsequent sorting criteria.

A then_by operation can only be applied to a order_by range.

Applying this operator to another kind of range will result in a compile-time error.

Signature
template <typename TKeySelector>
constexpr auto then_by( TKeySelector&& key_selector, sort_direction sort_dir ) const;
Example
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const auto words = std::vector{ "hello"s, "world"s, "here"s,
                                "are"s, "some"s, "sorted"s, "words"s };

const auto result = linq::from( &words )
                   .order_by_ascending( linq::size )  // convenience function ..._by_ascending
                   .then_by_ascending( linq::self )   // same here, but with then_by
                   .to_vector();

assert( result == std::vector{ "are"s, "here"s, "some"s,
                               "hello"s, "words"s, "world"s, "sorted"s } );

reverse

Reverses the order of the range.

Signature
constexpr auto reverse() const;
Example
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const auto numbers = std::vector{ 1, 2, 3, 4 };

const auto result = linq::from( &numbers )
                   .reverse()
                   .to_vector();

assert( result.size() == 4 );
assert( result == std::vector{ 4, 3, 2, 1 } );