Next: , Previous: , Up: Vectors   [Contents][Index]

### 8.2 Selecting Vector Components

procedure: vector? object

Returns `#t` if object is a vector; otherwise returns `#f`.

procedure: vector-length vector

Returns the number of elements in vector.

procedure: vector-ref vector k

Returns the contents of element k of vector. K must be a valid index of vector.

```(vector-ref '#(1 1 2 3 5 8 13 21) 5)    ⇒  8
```
procedure: vector-set! vector k object

Stores object in element k of vector and returns an unspecified value. K must be a valid index of vector.

```(let ((vec (vector 0 '(2 2 2 2) "Anna")))
(vector-set! vec 1 '("Sue" "Sue"))
vec)
⇒  #(0 ("Sue" "Sue") "Anna")
```
procedure: vector-first vector
procedure: vector-second vector
procedure: vector-third vector
procedure: vector-fourth vector
procedure: vector-fifth vector
procedure: vector-sixth vector
procedure: vector-seventh vector
procedure: vector-eighth vector

These procedures access the first several elements of vector in the obvious way. It is an error if the implicit index of one of these procedurs is not a valid index of vector.

procedure: vector-binary-search vector key<? unwrap-key key

Searches vector for an element with a key matching key, returning the element if one is found or `#f` if none. The search operation takes time proportional to the logarithm of the length of vector. Unwrap-key must be a procedure that maps each element of vector to a key. Key<? must be a procedure that implements a total ordering on the keys of the elements.

```(define (translate number)
(vector-binary-search '#((1 . i)
(2 . ii)
(3 . iii)
(6 . vi))
< car number))
(translate 2)  ⇒  (2 . ii)
(translate 4)  ⇒  #F
```

Next: Cutting Vectors, Previous: Construction of Vectors, Up: Vectors   [Contents][Index]