3.9 Vectors

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▼ | 3 | Built-In Datatypes

3.1 | Booleans
3.2 | Numbers
3.3 | Characters
3.4 | Strings (Unicode)
3.5 | Bytes and Byte Strings
3.6 | Symbols
3.7 | Keywords
3.8 | Pairs and Lists
3.9 | Vectors
3.10 | Hash Tables
3.11 | Boxes
3.12 | Void and Undefined

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### 3.9 Vectors🔗ℹ

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 The Racket Reference documents the fine points of the syntax of vectors.

Examples:

> > #("a" "b" "c")
> '#("a" "b" "c")
> > #(name (that tune))
> '#(name (that tune))
> > #4(baldwin bruce)
> '#(baldwin bruce bruce bruce)
> > (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.

Vectors can be converted to lists and vice versa via vector->list and list->vector; 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:

> > (list->vector (map string-titlecase
> (vector->list #("three" "blind" "mice"))))
> '#("Three" "Blind" "Mice")

> > > Vectors in The Racket Reference provides more on vectors and vector procedures.

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