v/vlib/arrays/arrays.v

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module arrays
// Common arrays functions:
// - min / max - return the value of the minumum / maximum
// - idx_min / idx_max - return the index of the first minumum / maximum
// - merge - combine two sorted arrays and maintain sorted order
// - chunk - chunk array to arrays with n elements
// - window - get snapshots of the window of the given size sliding along array with the given step, where each snapshot is an array
// - zip - concat two arrays into one map
// min returns the minimum value in the array
pub fn min<T>(a []T) ?T {
if a.len == 0 {
return error('.min called on an empty array')
}
mut val := a[0]
for e in a {
if e < val {
val = e
}
}
return val
}
// max returns the maximum the maximum value in the array
pub fn max<T>(a []T) ?T {
if a.len == 0 {
return error('.max called on an empty array')
}
mut val := a[0]
for e in a {
if e > val {
val = e
}
}
return val
}
// idx_min returns the index of the minimum value in the array
pub fn idx_min<T>(a []T) ?int {
if a.len == 0 {
return error('.idx_min called on an empty array')
}
mut idx := 0
mut val := a[0]
for i, e in a {
if e < val {
val = e
idx = i
}
}
return idx
}
// idx_max returns the index of the maximum value in the array
pub fn idx_max<T>(a []T) ?int {
if a.len == 0 {
return error('.idx_max called on an empty array')
}
mut idx := 0
mut val := a[0]
for i, e in a {
if e > val {
val = e
idx = i
}
}
return idx
}
// merge two sorted arrays (ascending) and maintain sorted order
[direct_array_access]
pub fn merge<T>(a []T, b []T) []T {
mut m := []T{len: a.len + b.len}
mut ia := 0
mut ib := 0
mut j := 0
// TODO efficient approach to merge_desc where: a[ia] >= b[ib]
for ia < a.len && ib < b.len {
if a[ia] <= b[ib] {
m[j] = a[ia]
ia++
} else {
m[j] = b[ib]
ib++
}
j++
}
// a leftovers
for ia < a.len {
m[j] = a[ia]
ia++
j++
}
// b leftovers
for ib < b.len {
m[j] = b[ib]
ib++
j++
}
return m
}
// group n arrays into a single array of arrays with n elements
pub fn group<T>(lists ...[]T) [][]T {
mut length := if lists.len > 0 { lists[0].len } else { 0 }
// calculate length of output by finding shortest input array
for ndx in 1 .. lists.len {
if lists[ndx].len < length {
length = lists[ndx].len
}
}
if length > 0 {
mut arr := [][]T{cap: length}
// append all combined arrays into the resultant array
for ndx in 0 .. length {
mut zipped := []T{cap: lists.len}
// combine each list item for the ndx position into one array
for list_ndx in 0 .. lists.len {
zipped << lists[list_ndx][ndx]
}
arr << zipped
}
return arr
}
return [][]T{}
}
// chunk array to arrays with n elements
// example: arrays.chunk([1, 2, 3], 2) => [[1, 2], [3]]
pub fn chunk<T>(list []T, size int) [][]T {
// allocate chunk array
mut chunks := [][]T{cap: list.len / size + if list.len % size == 0 { 0 } else { 1 }}
for i := 0; true; {
// check chunk size is greater than remaining element size
if list.len < i + size {
// check if there's no more element to chunk
if list.len <= i {
break
}
chunks << list[i..]
break
}
chunks << list[i..i + size]
i += size
}
return chunks
}
pub struct WindowAttribute {
size int
step int = 1
}
// get snapshots of the window of the given size sliding along array with the given step, where each snapshot is an array.
// - `size` - snapshot size
// - `step` - gap size between each snapshot, default is 1.
//
// example A: `arrays.window([1, 2, 3, 4], size: 2)` => `[[1, 2], [2, 3], [3, 4]]`
// example B: `arrays.window([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], size: 3, step: 2)` => `[[1, 2, 3], [3, 4, 5], [5, 6, 7], [7, 8, 9]]`
pub fn window<T>(list []T, attr WindowAttribute) [][]T {
// allocate snapshot array
mut windows := [][]T{cap: list.len - attr.size + 1}
for i := 0; true; {
// check remaining elements size is less than snapshot size
if list.len < i + attr.size {
break
}
windows << list[i..i + attr.size]
i += attr.step
}
return windows
}
// sum up array, return nothing when array has no elements
// NOTICE: currently V has bug that cannot make sum function takes custom struct with + operator overloaded.
// which means you can only pass array of numbers for now.
// Future work: Fix generic operator overloading detection issue.
// usage: `arrays.sum<int>([1, 2, 3, 4, 5])?` => `15`
pub fn sum<T>(list []T) ?T {
if list.len == 0 {
return error('Cannot sum up array of nothing.')
} else {
mut head := list[0]
for i, e in list {
if i == 0 {
continue
} else {
head += e
}
}
return head
}
}
// accumulates values with the first element and applying providing operation to current accumulator value and each elements.
// if the array is empty, then returns error.
// usage: `arrays.reduce([1, 2, 3, 4, 5], fn (t1 int, t2 int) int { return t1 * t2 })?` => `120`
pub fn reduce<T>(list []T, reduce_op fn (t1 T, t2 T) T) ?T {
if list.len == 0 {
return error('Cannot reduce array of nothing.')
} else {
mut value := list[0]
for i, e in list {
if i == 0 {
continue
} else {
value = reduce_op(value, e)
}
}
return value
}
}
// accumulates values with providing initial value and applying providing operation to current accumulator value and each elements.
// usage: `arrays.fold<string, byte>(['H', 'e', 'l', 'l', 'o'], 0, fn (r int, t string) int { return r + t[0] })` => `149`
pub fn fold<T, R>(list []T, init R, fold_op fn (r R, t T) R) R {
mut value := init
for e in list {
value = fold_op(value, e)
}
return value
}
// flattens n + 1 dimensional array into n dimensional array
// usage: `arrays.flatten<int>([[1, 2, 3], [4, 5]])` => `[1, 2, 3, 4, 5]`
pub fn flatten<T>(list [][]T) []T {
// calculate required capacity
mut required_size := 0
for e1 in list {
for _ in e1 {
required_size += 1
}
}
// allocate flattened array
mut result := []T{cap: required_size}
for e1 in list {
for e2 in e1 {
result << e2
}
}
return result
}
// grouping list of elements with given key selector.
// usage: `arrays.assort<int, string>(['H', 'el', 'lo'], fn (v string) int { return v.len })` => `{1: ['H'], 2: ['el', 'lo']}`
pub fn group_by<K, V>(list []V, grouping_op fn (v V) K) map[K][]V {
mut result := map[K][]V{}
for v in list {
key := grouping_op(v)
// check if key exists, if not, then create a new array with matched value, otherwise append.
if key in result {
result[key] << v
} else {
result[key] = [v]
}
}
return result
}
// concatenate two arrays
pub fn concat<T>(a []T, b ...T) []T {
mut m := []T{cap: a.len + b.len}
m << a
m << b
return m
}
// returns the smallest element >= val, requires `arr` to be sorted
pub fn lower_bound<T>(arr []T, val T) ?T {
if arr.len == 0 {
return error('.lower_bound called on an empty array')
}
mut left, mut right := 0, arr.len - 1
for ; left <= right; {
idx := (left + right) / 2
elem := arr[idx]
if elem < val {
left = idx + 1
} else {
right = idx - 1
}
}
if left >= arr.len {
return error('')
} else {
return arr[left]
}
}
// returns the largest element <= val, requires `arr` to be sorted
pub fn upper_bound<T>(arr []T, val T) ?T {
if arr.len == 0 {
return error('.upper_bound called on an empty array')
}
mut left, mut right := 0, arr.len - 1
for ; left <= right; {
idx := (left + right) / 2
elem := arr[idx]
if elem > val {
right = idx - 1
} else {
left = idx + 1
}
}
if right < 0 {
return error('')
} else {
return arr[right]
}
}
// binary search, requires `arr` to be sorted, returns index
pub fn binary_search<T>(arr []T, target T) ?int {
mut left := 0
mut right := arr.len - 1
for ; left <= right; {
idx := (left + right) / 2
elem := arr[idx]
if elem == target {
return idx
}
if elem < target {
left = idx + 1
} else {
right = idx - 1
}
}
return error('')
}