# SRFI 133 - Vector Library

The `(srfi 133)` provides a vector library.

# vector-unfold

``````(vector-unfold f length initial-seed ...) -> vector
``````

The fundamental vector constructor. Creates a vector whose length is `length` and iterates across each index `k` between `0` and `length`, applying `f` at each iteration to the current index and current seeds, in that order, to receive n + 1 values: first, the element to put in the kth slot of the new vector and n new seeds for the next iteration. It is an error for the number of seeds to vary between iterations. Note that the termination condition is different from the `unfold` procedure of SRFI 1.

Examples:

``````(vector-unfold (λ (i x) (values x (- x 1)))
10 0)
#(0 -1 -2 -3 -4 -5 -6 -7 -8 -9)
``````

Construct a vector of the sequence of integers in the range [0,n).

``````(vector-unfold values n)
#(0 1 2 ... n-2 n-1)
``````

Copy vector.

``````(vector-unfold (λ (i) (vector-ref vector i))
(vector-length vector))
``````

# vector-unfold-right

``````(vector-unfold-right f length initial-seed ...) -> vector
``````

Like `vector-unfold`, but it uses `f` to generate elements from right-to-left, rather than left-to-right. The first `index` used is `length - 1`. Note that the termination condition is different from the `unfold-right` procedure of SRFI 1.

Examples:

Construct a vector of pairs of non-negative integers whose values sum to 4.

``````(vector-unfold-right (λ (i x) (values (cons i x) (+ x 1))) 5 0)
#((0 . 4) (1 . 3) (2 . 2) (3 . 1) (4 . 0))
``````

Reverse vector.

``````(vector-unfold-right (λ (i x) (values (vector-ref vector x) (+ x 1)))
(vector-length vector)
0)
``````

# vector-reverse-copy

``````(vector-reverse-copy vec [start [end]]) -> vector
``````

Like `vector-copy`, but it copies the elements in the reverse order from `vec`.

Example:

``````(vector-reverse-copy '#(5 4 3 2 1 0) 1 5)
#(1 2 3 4)
``````

# vector-concatenate

``````(vector-concatenate list-of-vectors) -> vector
``````

Appends each vector in `list-of-vectors`. This is equivalent to:

``````(apply vector-append list-of-vectors)
``````

However, it may be implemented better.

Example:

``````(vector-concatenate '(#(a b) #(c d)))
#(a b c d)
``````

# vector-append-subvectors

``````(vector-append-subvectors [vec start end] ...) -> vector
``````

Returns a vector that contains every element of each `vec` from `start` to `end` in the specified order. This procedure is a generalization of `vector-append`.

Example:

``````(vector-append-subvectors '#(a b c d e) 0 2 '#(f g h i j) 2 4)
#(a b h i)
``````

# vector-empty?

``````(vector-empty? vec) -> boolean
``````

Returns `#t` if `vec` is empty, i.e. its length is `0`, and `#f` if not.

# vector=

``````(vector= elt=? vec ...) -> boolean
``````

Vector structure comparator, generalized across user-specified element comparators. Vectors `a` and `b` are considered equal by `vector=` iff their lengths are the same, and for each respective element `Ea` and `Eb`, `(elt=? Ea Eb)` returns a true value. `Elt=?` is always applied to two arguments.

If there are only zero or one vector arguments, `#t` is automatically returned. The dynamic order in which comparisons of elements and of vectors are performed is left completely unspecified; do not rely on a particular order.

Examples:

``````(vector= eq? '#(a b c d) '#(a b c d))
#t

(vector= eq? '#(a b c d) '#(a b d c))
#f

(vector= = '#(1 2 3 4 5) '#(1 2 3 4))
#f

(vector= = '#(1 2 3 4) '#(1 2 3 4))
#t
``````

The two trivial cases.

``````(vector= eq?)
#t

(vector= eq? '#(a))
#t
``````

Note the fact that we don’t use vector literals in the next two. It is unspecified whether or not literal vectors with the same external representation are `eq?`.

``````(vector= eq? (vector (vector 'a)) (vector (vector 'a)))
#f

(vector= equal? (vector (vector 'a)) (vector (vector 'a)))
#t
``````

# vector-fold

``````(vector-fold kons knil vec1 vec2 ...) -> value
``````

The fundamental vector iterator. `Kons` is iterated over each value in all of the vectors, stopping at the end of the shortest; `kons` is applied as `(kons state (vector-ref vec1 i) (vector-ref vec2 i) ...)` where `state` is the current state value. The current state value begins with `knil`, and becomes whatever `kons` returned on the previous iteration, and `i` is the current index.

The iteration is strictly left-to-right.

Examples:

Find the longest string’s length in `vector-of-strings`.

``````(vector-fold (λ (len str) (max (string-length str) len))
0 vector-of-strings)
``````

Produce a list of the reversed elements of `vec`.

``````(vector-fold (λ (tail elt) (cons elt tail))
'() vec)
``````

Count the number of even numbers in `vec`.

``````(vector-fold (λ (counter n)
(if (even? n) (+ counter 1) counter))
0 vec)
``````

# vector-fold-right

``````(vector-fold-right kons knil vec1 vec2 ...) -> value
``````

Similar to `vector-fold`, but it iterates right to left instead of left to right.

Example:

Convert a vector to a list.

``````(vector-fold-right (λ (tail elt) (cons elt tail))
'() '#(a b c d))
(a b c d)
``````

# vector-map!

``````(vector-map! f vec1 vec2 ...) -> unspecified
``````

Similar to `vector-map`, but rather than mapping the new elements into a new vector, the new mapped elements are destructively inserted into `vec1`. Again, the dynamic order of application of `f` is unspecified, so it is dangerous for `f` to apply either `vector-ref` or `vector-set!` to `vec1` in `f`.

# vector-count

``````(vector-count pred? vec1 vec2 ...) -> exact nonnegative integer
``````

Counts the number of parallel elements in the vectors that satisfy `pred?`, which is applied, for each index `i` in the range [0, length) where `length` is the length of the smallest vector argument, to each parallel element in the vectors, in order.

Examples:

``````(vector-count even? '#(3 1 4 1 5 9 2 5 6))
3

(vector-count < '#(1 3 6 9) '#(2 4 6 8 10 12))
2
``````

# vector-cumulate

``````(vector-cumulate f knil vec) -> vector
``````

Returns a newly allocated vector `new` with the same length as `vec`. Each element `i` of `new` is set to the result of invoking `f` on `newi-1` and `veci`, except that for the first call on `f`, the first argument is `knil`. The new vector is returned.

Example:

``````(vector-cumulate + 0 '#(3 1 4 1 5 9 2 5 6))
#(3 4 8 9 14 23 25 30 36)
``````

# vector-index

``````(vector-index pred? vec1 vec2 ...) -> exact nonnegative integer or #f
``````

Finds & returns the index of the first elements in `vec1 vec2 ...` that satisfy `pred?`. If no matching element is found by the end of the shortest vector, `#f` is returned.

Examples:

``````(vector-index even? '#(3 1 4 1 5 9))
2

(vector-index < '#(3 1 4 1 5 9 2 5 6) '#(2 7 1 8 2))
1

(vector-index = '#(3 1 4 1 5 9 2 5 6) '#(2 7 1 8 2))
#f
``````

# vector-index-right

``````(vector-index-right pred? vec1 vec2 ...) -> exact nonnegative integer or #f
``````

Like `vector-index`, but it searches right-to-left, rather than left-to-right, and all of the vectors must have the same length.

# vector-skip

``````(vector-skip pred? vec1 vec2 ...) -> exact nonnegative integer or #f
``````

Finds & returns the index of the first elements in `vec1 vec2 ...` that do not satisfy `pred?`. If all the values in the vectors satisfy `pred?` until the end of the shortest vector, this returns `#f`. This is equivalent to:

``````(vector-index (λ (x1 x2 ...) (not (pred? x1 x1 ...)))
vec1 vec2 ...)
``````

Example:

``````(vector-skip number? '#(1 2 a b 3 4 c d))
2
``````

# vector-skip-right

``````(vector-skip-right pred? vec1 vec2 ...) -> exact nonnegative integer or #f
``````

Like `vector-skip`, but it searches for a non-matching element right-to-left, rather than left-to-right, and it is an error if all of the vectors do not have the same length. This is equivalent to:

``````(vector-index-right (λ (x1 x2 ...) (not (pred? x1 x1 ...)))
vec1 vec2 ...)
``````

# vector-binary-search

``````(vector-binary-search vec value cmp) -> exact nonnegative integer or #f
``````

Similar to `vector-index` and `vector-index-right`, but instead of searching left to right or right to left, this performs a binary search. If there is more than one element of `vec` that matches value in the sense of `cmp`, `vector-binary-search` may return the index of any of them.

`cmp` should be a procedure of two arguments and return a negative integer, which indicates that its first argument is less than its second, zero, which indicates that they are equal, or a positive integer, which indicates that the first argument is greater than the second argument. An example `cmp` might be:

``````(lambdaλ (char1 char2)
(cond ((char<? char1 char2) -1)
((char=? char1 char2) 0)
(else 1)))
``````

# vector-any

``````(vector-any pred? vec1 vec2 ...) -> value or #f
``````

Finds the first set of elements in parallel from `vec1 vec2 ...` for which `pred?` returns a true value. If such a parallel set of elements exists, `vector-any` returns the value that `pred?` returned for that set of elements. The iteration is strictly left-to-right.

# vector-every

``````(vector-every pred? vec1 vec2 ...) -> value or #f
``````

If, for every index `i` between `0` and the length of the shortest vector argument, the set of elements `(vector-ref vec1 i) (vector-ref vec2 i) ...` satisfies `pred?`, `vector-every` returns the value that `pred?` returned for the last set of elements, at the last index of the shortest vector. The iteration is strictly left-to-right.

# vector-partition

``````(vector-partition pred? vec) -> vector and integer
``````

A vector the same size as `vec` is newly allocated and filled with all the elements of `vec` that satisfy `pred?` in their original order followed by all the elements that do not satisfy `pred?`, also in their original order.

Two values are returned, the newly allocated vector and the index of the leftmost element that does not satisfy `pred?`.

# vector-swap!

``````(vector-swap! vec i j) -> unspecified
``````

Swaps or exchanges the values of the locations in `vec` at `i` & `j`.

# vector-reverse!

``````(vector-reverse! vec [start [end]]) -> unspecified
``````

Destructively reverses the contents of the sequence of locations in `vec` between `start` and `end`. Start defaults to `0` and `end` defaults to the length of `vec`. Note that this does not deeply reverse.

# vector-reverse-copy!

``````(vector-reverse-copy! to at from [start [end]]) -> unspecified
``````

Like `vector-copy!`, but the elements appear in to in reverse order.

# vector-unfold!

``````(vector-unfold! f vec start end initial-seed ...) -> unspecified
``````

Like `vector-unfold`, but the elements are copied into the vector `vec` starting at element `start` rather than into a newly allocated vector. Terminates when `end-start` elements have been generated.

# vector-unfold-right!

``````(vector-unfold-right! f vec start end initial-seed ...) -> unspecified
``````

`Like `vector-unfold!`, but the elements are copied in reverse order into the vector `vec` starting at the index preceding `end`.

# reverse-vector->list

``````(reverse-vector->list vec [start [end]]) -> proper-list
``````

Like `vector->list`, but the resulting list contains the elements in reverse of `vec`.

# reverse-list->vector

``````(reverse-list->vector proper-list) -> vector
``````

Like `list->vector`, but the resulting vector contains the elements in reverse of `proper-list`.