3.9 Vectors
A vector is a fixed-length array of arbitrary values. Unlike a list, a vector supports constant-time access and update of its elements.
A vector prints similar to a list – as a parenthesized sequence of its elements – but a vector is prefixed with # after ', or it uses vector if one of its elements cannot be expressed with quote.
For a vector as an expression, an optional length can be supplied. Also, a vector as an expression implicitly quotes the forms for its content, which means that identifiers and parenthesized forms in a vector constant represent symbols and lists.
Reading Vectors in Reference: Racket documents the fine points of the syntax of vectors.
Examples: |
> #("a" "b" "c") |
'#("a" "b" "c") |
> #(name (that tune)) |
'#(name (that tune)) |
> (vector-ref #("a" "b" "c") 1) |
"b" |
> (vector-ref #(name (that tune)) 1) |
'(that tune) |
Like strings, a vector is either mutable or immutable, and vectors written directly as expressions are immutable.
Vector can be converted to lists and vice versa via list->vector and vector->list; such conversions are particularly useful in combination with predefined procedures on lists. When allocating extra lists seems too expensive, consider using looping forms like for/fold, which recognize vectors as well as lists.
Example: | ||
| ||
'#("Three" "Blind" "Mice") |
Vectors in Reference: Racket provides more on vectors and vector procedures.