► |  | Guide: Racket

1 | Welcome to Racket
2 | Racket Essentials
3 | Built-In Datatypes
4 | Expressions and Definitions
5 | Programmer-Defined Datatypes
6 | Modules
7 | Contracts
8 | Input and Output
9 | Regular Expressions
10 | Exceptions and Control
11 | Iterations and Comprehensions
12 | Pattern Matching
13 | Classes and Objects
14 | Units (Components)
15 | Reflection and Dynamic Evaluation
16 | Macros
17 | Creating Languages
18 | Performance
19 | Running and Creating Executables
20 | Compilation and Configuration
21 | More Libraries
22 | Dialects of Racket and Scheme
| Bibliography
| Index

▼ | 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

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:

> ( list->vector ( map string-titlecase
( vector->list #("three" "blind" "mice"))))

'#("Three" "Blind" "Mice")

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

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