Sorting algorithm

An example of stable sorting on playing cards. When the cards are sorted by rank with a stable sort, the two 5s must remain in the same order in the sorted output that they were originally in. When they are sorted with a non-stable sort, the 5s may end up in the opposite order in the sorted output.

A sorting algorithm is an algorithm that puts the elements of a collection into a certain order. Most commonly, numbers are sorted by their value, and words are sorted by their lexicographic order (as they would appear in a dictionary or phone book). Efficient sorting is important for other things: finding an element in a sorted collection is easier, and merging a new element may also be easier if the collection is sorted.

Sorting needs to take different into account that in some cases, the data can only be read sequentially, like on a tape.