# SRFI 133 - Vector Library The `(srfi 133)` provides a vector library. See the [SRFI document](http://srfi.schemers.org/srfi-133/srfi-133.html) for more information. ## Constructors [`vector-unfold`](#vector-unfold) [`vector-unfold-right`](#vector-unfold-right) [`vector-reverse-copy`](#vector-reverse-copy) [`vector-concatenate`](#vector-concatenate) [`vector-append-subvectors`](#vector-append-subvectors) ## Predicates [`vector-empty?`](#vector-empty) [`vector=`](#vector) ## Iteration [`vector-fold`](#vector-fold) [`vector-fold-right`](#vector-fold-right) [`vector-map!`](#vector-map) [`vector-count`](#vector-count) [`vector-cumulate`](#vector-cumulate) ## Searching [`vector-index`](#vector-index) [`vector-index-right`](#vector-index-right) [`vector-skip`](#vector-skip) [`vector-skip-right`](#vector-skip-right) [`vector-binary-search`](#vector-binary-search) [`vector-any`](#vector-any) [`vector-every`](#vector-every) [`vector-partition`](#vector-partition) ## Mutators [`vector-swap!`](#vector-swap) [`vector-reverse!`](#vector-reverse) [`vector-reverse-copy!`](#vector-reverse-copy) [`vector-unfold!`](#vector-unfold) [`vector-unfold-right!`](#vector-unfold-right) ## Conversion [`reverse-vector->list`](#reverse-vector-list) [`reverse-list->vector`](#reverse-list-vector) # 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 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`.