### 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