# std/sequtils

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Although this module has `seq` in its name, it implements operations not only for the seq type, but for three built-in container types under the `openArray` umbrella:

- sequences
- strings
- array

The `system` module defines several common functions, such as:

- `newSeq[T]` for creating new sequences of type `T`
- `@` for converting arrays and strings to sequences
- `add` for adding new elements to strings and sequences
- `&` for string and seq concatenation
- `in` (alias for `contains`) and `notin` for checking if an item is in a container

This module builds upon that, providing additional functionality in form of procs, iterators and templates inspired by functional programming languages.

For functional style programming you have different options at your disposal:

- the sugar.collect macro
- pass an anonymous proc
- import the sugar module and use the => macro
- use ...It templates (mapIt, filterIt, etc.)

Chaining of functions is possible thanks to the method call syntax.

Example:

    import std/sequtils
    import std/sugar

    # Creating a sequence from 1 to 10, multiplying each member by 2,
    # keeping only the members which are not divisible by 6.
    let
      foo = toSeq(1..10).map(x => x * 2).filter(x => x mod 6 != 0)
      bar = toSeq(1..10).mapIt(it * 2).filterIt(it mod 6 != 0)
      baz = collect:
        for i in 1..10:
          let j = 2 * i
          if j mod 6 != 0:
            j

    doAssert foo == bar
    doAssert foo == baz
    doAssert foo == @[2, 4, 8, 10, 14, 16, 20]

    doAssert foo.any(x => x > 17)
    doAssert not bar.allIt(it < 20)
    doAssert foo.foldl(a + b) == 74 # sum of all members

Example:

    import std/sequtils
    from std/strutils import join

    let
      vowels = @"aeiou"
      foo = "sequtils is an awesome module"

    doAssert (vowels is seq[char]) and (vowels == @['a', 'e', 'i', 'o', 'u'])
    doAssert foo.filterIt(it notin vowels).join == "sqtls s n wsm mdl"

# See also

- strutils module for common string functions
- sugar module for syntactic sugar macros
- algorithm module for common generic algorithms
- json module for a structure which allows heterogeneous members

# Imports

since, macros, typetraits, assertions

# Procs

    func addUnique[T](s: var seq[T]; x: sink T)

  Adds `x` to the container `s` if it is not already present. Uses `==` to check if the item is already present.

  Example:

      var a = @[1, 2, 3]
      a.addUnique(4)
      a.addUnique(4)
      assert a == @[1, 2, 3, 4]

  Source Edit

    proc all[T](s: openArray[T]; pred: proc (x: T): bool {.closure.}): bool {.
        effectsOf: pred.}

  Iterates through a container and checks if every item fulfills the predicate.

  See also:

  - allIt template
  - any proc

  Example:

      let numbers = @[1, 4, 5, 8, 9, 7, 4]
      assert all(numbers, proc (x: int): bool = x < 10) == true
      assert all(numbers, proc (x: int): bool = x < 9) == false

  Source Edit

    proc any[T](s: openArray[T]; pred: proc (x: T): bool {.closure.}): bool {.
        effectsOf: pred.}

  Iterates through a container and checks if at least one item fulfills the predicate.

  See also:

  - anyIt template
  - all proc

  Example:

      let numbers = @[1, 4, 5, 8, 9, 7, 4]
      assert any(numbers, proc (x: int): bool = x > 8) == true
      assert any(numbers, proc (x: int): bool = x > 9) == false

  Source Edit

    proc apply[T](s: openArray[T]; op: proc (x: T) {.closure.}) {.inline,
        effectsOf: op.}

  Same as `apply` but for a proc that does not return anything and does not mutate `s` directly.

  Example:

      var message: string
      apply([0, 1, 2, 3, 4], proc(item: int) = message.addInt item)
      assert message == "01234"

  Source Edit

    proc apply[T](s: var openArray[T]; op: proc (x: T): T {.closure.}) {.inline,
        effectsOf: op.}

  Applies `op` to every item in `s` modifying it directly.

  Note that the container `s` must be declared as a `var` and it is required for your input and output types to be the same, since `s` is modified in-place. The parameter function takes and returns a `T` type variable.

  See also:

  - applyIt template
  - map proc

  Example:

      var a = @["1", "2", "3", "4"]
      apply(a, proc(x: string): string = x & "42")
      assert a == @["142", "242", "342", "442"]

  Source Edit

    proc apply[T](s: var openArray[T]; op: proc (x: var T) {.closure.}) {.inline,
        effectsOf: op.}

  Applies `op` to every item in `s`, modifying it directly.

  Note that the container `s` must be declared as a `var`, since `s` is modified in-place. The parameter function takes a `var T` type parameter.

  See also:

  - applyIt template
  - map proc

  Example:

      var a = @["1", "2", "3", "4"]
      apply(a, proc(x: var string) = x &= "42")
      assert a == @["142", "242", "342", "442"]

  Source Edit

    func concat[T](seqs: varargs[seq[T]]): seq[T]

  Takes several sequences' items and returns them inside a new sequence. All sequences must be of the same type.

  See also:

  - distribute func for a reverse operation

  Example:

      let
        s1 = @[1, 2, 3]
        s2 = @[4, 5]
        s3 = @[6, 7]
        total = concat(s1, s2, s3)
      assert total == @[1, 2, 3, 4, 5, 6, 7]

  Source Edit

    func count[T](s: openArray[T]; x: T): int

  Returns the number of occurrences of the item `x` in the container `s`.

  Example:

      let
        a = @[1, 2, 2, 3, 2, 4, 2]
        b = "abracadabra"
      assert count(a, 2) == 4
      assert count(a, 99) == 0
      assert count(b, 'r') == 2

  Source Edit

    func cycle[T](s: openArray[T]; n: Natural): seq[T]

  Returns a new sequence with the items of the container `s` repeated `n` times. `n` must be a non-negative number (zero or more).

  Example:

      let
        s = @[1, 2, 3]
        total = s.cycle(3)
      assert total == @[1, 2, 3, 1, 2, 3, 1, 2, 3]

  Source Edit

    func deduplicate[T](s: openArray[T]; isSorted: bool = false): seq[T]

  Returns a new sequence without duplicates.

  Setting the optional argument `isSorted` to true (default: false) uses a faster algorithm for deduplication.

  Example:

      let
        dup1 = @[1, 1, 3, 4, 2, 2, 8, 1, 4]
        dup2 = @["a", "a", "c", "d", "d"]
        unique1 = deduplicate(dup1)
        unique2 = deduplicate(dup2, isSorted = true)
      assert unique1 == @[1, 3, 4, 2, 8]
      assert unique2 == @["a", "c", "d"]

  Source Edit

    func delete[T](s: var seq[T]; first, last: Natural) {.
        ...deprecated: "use `delete(s, first..last)`".}

  Deprecated: use `delete(s, first..last)`
  Deletes the items of a sequence `s` at positions `first..last` (including both ends of the range). This modifies `s` itself, it does not return a copy.

  Example: cmd: --warning:deprecated:off

      let outcome = @[1, 1, 1, 1, 1, 1, 1, 1]
      var dest = @[1, 1, 1, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1]
      dest.delete(3, 8)
      assert outcome == dest

  Source Edit

    func delete[T](s: var seq[T]; slice: Slice[int])

  Deletes the items `s[slice]`, raising `IndexDefect` if the slice contains elements out of range.

  This operation moves all elements after `s[slice]` in linear time.

  Example:

      var a = @[10, 11, 12, 13, 14]
      doAssertRaises(IndexDefect): a.delete(4..5)
      assert a == @[10, 11, 12, 13, 14]
      a.delete(4..4)
      assert a == @[10, 11, 12, 13]
      a.delete(1..2)
      assert a == @[10, 13]
      a.delete(1..<1) # empty slice
      assert a == @[10, 13]

  Source Edit

    func distribute[T](s: seq[T]; num: Positive; spread = true): seq[seq[T]]

  Splits and distributes a sequence `s` into `num` sub-sequences.

  Returns a sequence of `num` sequences. For some input values this is the inverse of the concat func. The input sequence `s` can be empty, which will produce `num` empty sequences.

  If `spread` is false and the length of `s` is not a multiple of `num`, the func will max out the first sub-sequence with `1 + len(s) div num` entries, leaving the remainder of elements to the last sequence.

  On the other hand, if `spread` is true, the func will distribute evenly the remainder of the division across all sequences, which makes the result more suited to multithreading where you are passing equal sized work units to a thread pool and want to maximize core usage.

  Example:

      let numbers = @[1, 2, 3, 4, 5, 6, 7]
      assert numbers.distribute(3) == @[@[1, 2, 3], @[4, 5], @[6, 7]]
      assert numbers.distribute(3, false) == @[@[1, 2, 3], @[4, 5, 6], @[7]]
      assert numbers.distribute(6)[0] == @[1, 2]
      assert numbers.distribute(6)[1] == @[3]

  Source Edit

    proc filter[T](s: openArray[T]; pred: proc (x: T): bool {.closure.}): seq[T] {.
        inline, effectsOf: pred.}

  Returns a new sequence with all the items of `s` that fulfill the predicate `pred` (a function that returns a `bool`).

  Instead of using `map` and `filter`, consider using the `collect` macro from the `sugar` module.

  See also:

  - sugar.collect macro
  - filterIt template
  - filter iterator
  - keepIf proc for the in-place version

  Example:

      let
        colors = @["red", "yellow", "black"]
        f1 = filter(colors, proc(x: string): bool = x.len < 6)
        f2 = filter(colors, proc(x: string): bool = x.contains('y'))
      assert f1 == @["red", "black"]
      assert f2 == @["yellow"]

  Source Edit

    func insert[T](dest: var seq[T]; src: openArray[T]; pos = 0)

  Inserts items from `src` into `dest` at position `pos`. This modifies `dest` itself, it does not return a copy.

  Note that the elements of `src` and `dest` must be of the same type.

  Example:

      var dest = @[1, 1, 1, 1, 1, 1, 1, 1]
      let
        src = @[2, 2, 2, 2, 2, 2]
        outcome = @[1, 1, 1, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1]
      dest.insert(src, 3)
      assert dest == outcome

  Source Edit

    proc keepIf[T](s: var seq[T]; pred: proc (x: T): bool {.closure.}) {.inline,
        effectsOf: pred.}

  Keeps the items in the passed sequence `s` if they fulfill the predicate `pred` (a function that returns a `bool`).

  Note that `s` must be declared as a `var`.

  Similar to the filter proc, but modifies the sequence directly.

  See also:

  - keepItIf template
  - filter proc

  Example:

      var floats = @[13.0, 12.5, 5.8, 2.0, 6.1, 9.9, 10.1]
      keepIf(floats, proc(x: float): bool = x > 10)
      assert floats == @[13.0, 12.5, 10.1]

  Source Edit

    proc map[T, S](s: openArray[T]; op: proc (x: T): S {.closure.}): seq[S] {.
        inline, effectsOf: op.}

  Returns a new sequence with the results of the `op` proc applied to every item in the container `s`.

  Since the input is not modified, you can use it to transform the type of the elements in the input container.

  Instead of using `map` and `filter`, consider using the `collect` macro from the `sugar` module.

  See also:

  - sugar.collect macro
  - mapIt template
  - apply proc for the in-place version

  Example:

      let
        a = @[1, 2, 3, 4]
        b = map(a, proc(x: int): string = $x)
      assert b == @["1", "2", "3", "4"]

  Source Edit

    proc max[T](x: openArray[T]; cmp: proc (a, b: T): int): T {.effectsOf: cmp.}

  The maximum value of `x`. Source Edit

    func maxIndex[T](s: openArray[T]): int

  Returns the index of the maximum value of `s`. `T` needs to have a `<` operator.

  Example:

      let
        a = @[1, 2, 3, 4]
        b = @[6, 5, 4, 3]
        c = [2, -7, 8, -5]
        d = "ziggy"
      assert maxIndex(a) == 3
      assert maxIndex(b) == 0
      assert maxIndex(c) == 2
      assert maxIndex(d) == 0

  Source Edit

    func maxIndex[T](s: openArray[T]; cmp: proc (a, b: T): int): int {.
        effectsOf: cmp.}

  Returns the index of the maximum value of `s`.

  Example:

      import std/sugar

      let s1 = @["foo","bar", "hello"]
      let s2 = @[2..4, 1..3, 6..10]
      assert maxIndex(s1, proc (a, b: string): int = a.len - b.len) == 2
      assert maxIndex(s2, (a, b) => a.a - b.a) == 2

  Source Edit

    proc min[T](x: openArray[T]; cmp: proc (a, b: T): int): T {.effectsOf: cmp.}

  The minimum value of `x`. Source Edit

    func minIndex[T](s: openArray[T]): int

  Returns the index of the minimum value of `s`. `T` needs to have a `<` operator.

  Example:

      let
        a = @[1, 2, 3, 4]
        b = @[6, 5, 4, 3]
        c = [2, -7, 8, -5]
        d = "ziggy"
      assert minIndex(a) == 0
      assert minIndex(b) == 3
      assert minIndex(c) == 1
      assert minIndex(d) == 2

  Source Edit

    func minIndex[T](s: openArray[T]; cmp: proc (a, b: T): int): int {.
        effectsOf: cmp.}

  Returns the index of the minimum value of `s`.

  Example:

      import std/sugar

      let s1 = @["foo","bar", "hello"]
      let s2 = @[2..4, 1..3, 6..10]
      assert minIndex(s1, proc (a, b: string): int = a.len - b.len) == 0
      assert minIndex(s2, (a, b) => a.a - b.a) == 1

  Source Edit

    func minmax[T](x: openArray[T]): (T, T)

  The minimum and maximum values of `x`. `T` needs to have a `<` operator. Source Edit

    func minmax[T](x: openArray[T]; cmp: proc (a, b: T): int): (T, T) {.
        effectsOf: cmp.}

  The minimum and maximum values of `x`. Source Edit

    proc repeat[T](x: T; n: Natural): seq[T]

  Returns a new sequence with the item `x` repeated `n` times. `n` must be a non-negative number (zero or more).

  Example:

      let
        total = repeat(5, 3)
      assert total == @[5, 5, 5]

  Source Edit

    proc unzip[S, T](s: openArray[(S, T)]): (seq[S], seq[T])

  Returns a tuple of two sequences split out from a sequence of 2-field tuples.

  Example:

      let
        zipped = @[(1, 'a'), (2, 'b'), (3, 'c')]
        unzipped1 = @[1, 2, 3]
        unzipped2 = @['a', 'b', 'c']
      assert zipped.unzip() == (unzipped1, unzipped2)
      assert zip(unzipped1, unzipped2).unzip() == (unzipped1, unzipped2)

  Source Edit

    proc zip[S, T](s1: openArray[S]; s2: openArray[T]): seq[(S, T)]

  Returns a new sequence with a combination of the two input containers.

  The input containers can be of different types. If one container is shorter, the remaining items in the longer container are discarded.

  Note: For Nim 1.0.x and older version, `zip` returned a seq of named tuples with fields `a` and `b`. For Nim versions 1.1.x and newer, `zip` returns a seq of unnamed tuples.

  Example:

      let
        short = @[1, 2, 3]
        long = @[6, 5, 4, 3, 2, 1]
        words = @["one", "two", "three"]
        letters = "abcd"
        zip1 = zip(short, long)
        zip2 = zip(short, words)
      assert zip1 == @[(1, 6), (2, 5), (3, 4)]
      assert zip2 == @[(1, "one"), (2, "two"), (3, "three")]
      assert zip1[2][0] == 3
      assert zip2[1][1] == "two"
      when (NimMajor, NimMinor) <= (1, 0):
        let
          zip3 = zip(long, letters)
        assert zip3 == @[(a: 6, b: 'a'), (5, 'b'), (4, 'c'), (3, 'd')]
        assert zip3[0].b == 'a'
      else:
        let
          zip3: seq[tuple[num: int, letter: char]] = zip(long, letters)
        assert zip3 == @[(6, 'a'), (5, 'b'), (4, 'c'), (3, 'd')]
        assert zip3[0].letter == 'a'

  Source Edit

# Iterators

    iterator filter[T](s: openArray[T]; pred: proc (x: T): bool {.closure.}): T {.
        effectsOf: pred.}

  Iterates through a container `s` and yields every item that fulfills the predicate `pred` (a function that returns a `bool`).

  Instead of using `map` and `filter`, consider using the `collect` macro from the `sugar` module.

  See also:

  - sugar.collect macro
  - filter proc
  - filterIt template

  Example:

      let numbers = @[1, 4, 5, 8, 9, 7, 4]
      var evens = newSeq[int]()
      for n in filter(numbers, proc (x: int): bool = x mod 2 == 0):
        evens.add(n)
      assert evens == @[4, 8, 4]

  Source Edit

    iterator items[T](xs: iterator (): T): T

  Iterates over each element yielded by a closure iterator. This may not seem particularly useful on its own, but this allows closure iterators to be used by the mapIt, filterIt, allIt, anyIt, etc. templates. Source Edit

# Macros

    macro mapLiterals(constructor, op: untyped; nested = true): untyped

  Applies `op` to each of the atomic literals like `3` or `"abc"` in the specified `constructor` AST. This can be used to map every array element to some target type:

  Example:

      let x = mapLiterals([0.1, 1.2, 2.3, 3.4], int)
      doAssert x is array[4, int]
      doAssert x == [int(0.1), int(1.2), int(2.3), int(3.4)]

  If `nested` is true (which is the default), the literals are replaced everywhere in the `constructor` AST, otherwise only the first level is considered:

  Example:

      let a = mapLiterals((1.2, (2.3, 3.4), 4.8), int)
      let b = mapLiterals((1.2, (2.3, 3.4), 4.8), int, nested=false)
      assert a == (1, (2, 3), 4)
      assert b == (1, (2.3, 3.4), 4)

      let c = mapLiterals((1, (2, 3), 4, (5, 6)), `$`)
      let d = mapLiterals((1, (2, 3), 4, (5, 6)), `$`, nested=false)
      assert c == ("1", ("2", "3"), "4", ("5", "6"))
      assert d == ("1", (2, 3), "4", (5, 6))

  There are no constraints for the `constructor` AST, it works for nested tuples of arrays of sets etc. Source Edit

# Templates

    template allIt(s, pred: untyped): bool

  Iterates through a container and checks if every item fulfills the predicate.

  Unlike the all proc, the predicate needs to be an expression using the `it` variable for testing, like: `allIt("abba", it == 'a')`.

  See also:

  - all proc
  - anyIt template

  Example:

      let numbers = @[1, 4, 5, 8, 9, 7, 4]
      assert numbers.allIt(it < 10) == true
      assert numbers.allIt(it < 9) == false

  Source Edit

    template anyIt(s, pred: untyped): bool

  Iterates through a container and checks if at least one item fulfills the predicate.

  Unlike the any proc, the predicate needs to be an expression using the `it` variable for testing, like: `anyIt("abba", it == 'a')`.

  See also:

  - any proc
  - allIt template

  Example:

      let numbers = @[1, 4, 5, 8, 9, 7, 4]
      assert numbers.anyIt(it > 8) == true
      assert numbers.anyIt(it > 9) == false

  Source Edit

    template applyIt(varSeq, op: untyped)

  Convenience template around the mutable `apply` proc to reduce typing.

  The template injects the `it` variable which you can use directly in an expression. The expression has to return the same type as the elements of the sequence you are mutating.

  See also:

  - apply proc
  - mapIt template

  Example:

      var nums = @[1, 2, 3, 4]
      nums.applyIt(it * 3)
      assert nums[0] + nums[3] == 15

  Source Edit

    template countIt(s, pred: untyped): int

  Returns a count of all the items that fulfill the predicate.

  The predicate needs to be an expression using the `it` variable for testing, like: `countIt(@[1, 2, 3], it > 2)`.

  Example:

      let numbers = @[-3, -2, -1, 0, 1, 2, 3, 4, 5, 6]
      iterator iota(n: int): int =
        for i in 0..<n: yield i
      assert numbers.countIt(it < 0) == 3
      assert countIt(iota(10), it < 2) == 2

  Source Edit

    template filterIt(s, pred: untyped): untyped

  Returns a new sequence with all the items of `s` that fulfill the predicate `pred`.

  Unlike the filter proc and filter iterator, the predicate needs to be an expression using the `it` variable for testing, like: `filterIt("abcxyz", it == 'x')`.

  Instead of using `mapIt` and `filterIt`, consider using the `collect` macro from the `sugar` module.

  See also:

  - sugar.collect macro
  - filter proc
  - filter iterator

  Example:

      let
        temperatures = @[-272.15, -2.0, 24.5, 44.31, 99.9, -113.44]
        acceptable = temperatures.filterIt(it < 50 and it > -10)
        notAcceptable = temperatures.filterIt(it > 50 or it < -10)
      assert acceptable == @[-2.0, 24.5, 44.31]
      assert notAcceptable == @[-272.15, 99.9, -113.44]

  Source Edit

    template findIt(s, predicate: untyped): int

  Iterates through a container and returns the index of the first item that fulfills the predicate, or -1

  Unlike the `find`, the predicate needs to be an expression using the `it` variable for testing, like: `findIt([3, 2, 1], it == 2)`.

  Source Edit

    template foldl(sequence, operation, first): untyped

  Template to fold a sequence from left to right, returning the accumulation.

  This version of `foldl` gets a starting parameter. This makes it possible to accumulate the sequence into a different type than the sequence elements.

  The `operation` parameter should be an expression which uses the variables `a` and `b` for each step of the fold. The `first` parameter is the start value (the first `a`) and therefore defines the type of the result.

  See also:

  - foldr template

  Example:

      let
        numbers = @[0, 8, 1, 5]
        digits = foldl(numbers, a & (chr(b + ord('0'))), "")
      assert digits == "0815"

  Source Edit

    template foldl(sequence, operation: untyped): untyped

  Template to fold a sequence from left to right, returning the accumulation.

  The sequence is required to have at least a single element. Debug versions of your program will assert in this situation but release versions will happily go ahead. If the sequence has a single element it will be returned without applying `operation`.

  The `operation` parameter should be an expression which uses the variables `a` and `b` for each step of the fold. Since this is a left fold, for non associative binary operations like subtraction think that the sequence of numbers 1, 2 and 3 will be parenthesized as (((1) - 2) - 3).

  See also:

  - foldl template with a starting parameter
  - foldr template

  Example:

      let
        numbers = @[5, 9, 11]
        addition = foldl(numbers, a + b)
        subtraction = foldl(numbers, a - b)
        multiplication = foldl(numbers, a * b)
        words = @["nim", "is", "cool"]
        concatenation = foldl(words, a & b)
        procs = @["proc", "Is", "Also", "Fine"]

      func foo(acc, cur: string): string =
        result = acc & cur

      assert addition == 25, "Addition is (((5)+9)+11)"
      assert subtraction == -15, "Subtraction is (((5)-9)-11)"
      assert multiplication == 495, "Multiplication is (((5)*9)*11)"
      assert concatenation == "nimiscool"
      assert foldl(procs, foo(a, b)) == "procIsAlsoFine"

  Source Edit

    template foldr(sequence, operation: untyped): untyped

  Template to fold a sequence from right to left, returning the accumulation.

  The sequence is required to have at least a single element. Debug versions of your program will assert in this situation but release versions will happily go ahead. If the sequence has a single element it will be returned without applying `operation`.

  The `operation` parameter should be an expression which uses the variables `a` and `b` for each step of the fold. Since this is a right fold, for non associative binary operations like subtraction think that the sequence of numbers 1, 2 and 3 will be parenthesized as (1 - (2 - (3))).

  See also:

  - foldl template
  - foldl template with a starting parameter

  Example:

      let
        numbers = @[5, 9, 11]
        addition = foldr(numbers, a + b)
        subtraction = foldr(numbers, a - b)
        multiplication = foldr(numbers, a * b)
        words = @["nim", "is", "cool"]
        concatenation = foldr(words, a & b)
      assert addition == 25, "Addition is (5+(9+(11)))"
      assert subtraction == 7, "Subtraction is (5-(9-(11)))"
      assert multiplication == 495, "Multiplication is (5*(9*(11)))"
      assert concatenation == "nimiscool"

  Source Edit

    template keepItIf(varSeq: seq; pred: untyped)

  Keeps the items in the passed sequence (must be declared as a `var`) if they fulfill the predicate.

  Unlike the keepIf proc, the predicate needs to be an expression using the `it` variable for testing, like: `keepItIf("abcxyz", it == 'x')`.

  See also:

  - keepIf proc
  - filterIt template

  Example:

      var candidates = @["foo", "bar", "baz", "foobar"]
      candidates.keepItIf(it.len == 3 and it[0] == 'b')
      assert candidates == @["bar", "baz"]

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    template mapIt(s: typed; op: untyped): untyped

  Returns a new sequence with the results of the `op` proc applied to every item in the container `s`.

  Since the input is not modified you can use it to transform the type of the elements in the input container.

  The template injects the `it` variable which you can use directly in an expression.

  Instead of using `mapIt` and `filterIt`, consider using the `collect` macro from the `sugar` module.

  See also:

  - sugar.collect macro
  - map proc
  - applyIt template for the in-place version

  Example:

      let
        nums = @[1, 2, 3, 4]
        strings = nums.mapIt($(4 * it))
      assert strings == @["4", "8", "12", "16"]

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    template newSeqWith(len: int; init: untyped): untyped

  Creates a new `seq` of length `len`, calling `init` to initialize each value of the seq.

  Useful for creating "2D" seqs - seqs containing other seqs or to populate fields of the created seq.

  Example:

      ## Creates a seq containing 5 bool seqs, each of length of 3.
      var seq2D = newSeqWith(5, newSeq[bool](3))
      assert seq2D.len == 5
      assert seq2D[0].len == 3
      assert seq2D[4][2] == false

      ## Creates a seq with random numbers
      import std/random
      var seqRand = newSeqWith(20, rand(1.0))
      assert seqRand[0] != seqRand[1]

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    template toSeq(iter: untyped): untyped

  Transforms any iterable (anything that can be iterated over, e.g. with a for-loop) into a sequence.

  Example:

      let
        myRange = 1..5
        mySet: set[int8] = {5'i8, 3, 1}
      assert typeof(myRange) is HSlice[system.int, system.int]
      assert typeof(mySet) is set[int8]

      let
        mySeq1 = toSeq(myRange)
        mySeq2 = toSeq(mySet)
      assert mySeq1 == @[1, 2, 3, 4, 5]
      assert mySeq2 == @[1'i8, 3, 5]

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