prepending

Prepending is the act of placing an item or sequence at the beginning of another sequence. In computing and data processing, prepending means creating a new structure by inserting at the front rather than at the end. The opposite operation is appending, which adds to the tail.

In linguistics, prepending can refer to prefixation, the attachment of a morpheme to the start of a word to modify its meaning or grammatical category. The term is also used more broadly to describe artificial or stylistic additions placed before a base form in text processing.

In data structures, prepending has different cost profiles. For example, adding an element to the front of a singly linked list is typically O(1), since it involves creating a new node that points to the current first element. In contrast, prepending to an array requires shifting all existing elements and is usually O(n). Some structures, such as deques, support fast prepend via dedicated operations.

Within programming languages, various idioms embody prepending: in Lisp, the cons operation constructs a new list by placing an element at the head; in Haskell, the colon operator does the same; in Python, prepend-like behavior can be achieved with [x] + lst or using insert(0, x), which is O(n). Understanding the performance characteristics helps guide data-structure choice and algorithm design.