distinct(xs)

Iterate through values skipping over those already encountered.

julia> for i in distinct([1,1,2,1,2,4,1,2,3,4])
           @show i
       end
i = 1
i = 2
i = 4
i = 3

groupby(f, xs)

Group consecutive values that share the same result of applying f.

julia> for i in groupby(x -> x[1], ["face", "foo", "bar", "book", "baz", "zzz"])
           @show i
       end
i = ["face", "foo"]
i = ["bar", "book", "baz"]
i = ["zzz"]

imap(f, xs1, [xs2, ...])

Iterate over values of a function applied to successive values from one or more iterators. Like Iterators.zip, the iterator is done when any of the input iterators have been exhausted.

julia> for i in imap(+, [1,2,3], [4,5,6])
            @show i
       end
i = 5
i = 7
i = 9

iterated(f, x)

Iterate over successive applications of f, as in x, f(x), f(f(x)), f(f(f(x))), ...

Use Base.Iterators.take() to obtain the required number of elements.

julia> for i in Iterators.take(iterated(x -> 2x, 1), 5)
           @show i
       end
i = 1
i = 2
i = 4
i = 8
i = 16

julia> for i in Iterators.take(iterated(sqrt, 100), 6)
           @show i
       end
i = 100
i = 10.0
i = 3.1622776601683795
i = 1.7782794100389228
i = 1.333521432163324
i = 1.1547819846894583

ncycle(iter, n)

Cycle through iter n times.

julia> for i in ncycle(1:3, 2)
           @show i
       end
i = 1
i = 2
i = 3
i = 1
i = 2
i = 3

nth(xs, n)

Return the nth element of xs. This is mostly useful for non-indexable collections.

julia> mersenne = Set([3, 7, 31, 127])
Set([7, 31, 3, 127])

julia> nth(mersenne, 3)
3

partition(xs, n, [step])

Group values into n-tuples.

julia> for i in partition(1:9, 3)
           @show i
       end
i = (1, 2, 3)
i = (4, 5, 6)
i = (7, 8, 9)

If the step parameter is set, each tuple is separated by step values.

julia> for i in partition(1:9, 3, 2)
           @show i
       end
i = (1, 2, 3)
i = (3, 4, 5)
i = (5, 6, 7)
i = (7, 8, 9)

julia> for i in partition(1:9, 3, 3)
           @show i
       end
i = (1, 2, 3)
i = (4, 5, 6)
i = (7, 8, 9)

julia> for i in partition(1:9, 2, 3)
           @show i
       end
i = (1, 2)
i = (4, 5)
i = (7, 8)

peekiter(xs)

Lets you peek at the head element of an iterator without updating the state.

julia> it = peekiter(["face", "foo", "bar", "book", "baz", "zzz"])
IterTools.PeekIter{Array{String,1}}(["face", "foo", "bar", "book", "baz", "zzz"])

julia> @show peek(it);
peek(it) = Some("face")

julia> @show peek(it);
peek(it) = Some("face")

julia> x, s = iterate(it)
("face", ("foo", 3))

julia> @show x;
x = "face"

julia> @show peek(it, s);
peek(it, s) = Some("foo")

repeatedly(f)
repeatedly(f, n)

Call function f n times, or infinitely if n is omitted.

julia> t() = (sleep(0.1); Dates.millisecond(now()))
t (generic function with 1 method)

julia> collect(repeatedly(t, 5))
5-element Array{Any,1}:
 993
  97
 200
 303
 408

takenth(xs, n)

Iterate through every nth element of xs.

julia> collect(takenth(5:15,3))
3-element Array{Int64,1}:
  7
 10
 13

subsets(xs)
subsets(xs, k)
subsets(xs, Val{k}())

Iterate over every subset of the indexable collection xs. You can restrict the subsets to a specific size k.

Giving the subset size in the form Val{k}() allows the compiler to produce code optimized for the particular size requested. This leads to performance comparable to hand-written loops if k is small and known at compile time, but may or may not improve performance otherwise.

julia> for i in subsets([1, 2, 3])
          @show i
       end
i = Int64[]
i = [1]
i = [2]
i = [1, 2]
i = [3]
i = [1, 3]
i = [2, 3]
i = [1, 2, 3]

julia> for i in subsets(1:4, 2)
          @show i
       end
i = [1, 2]
i = [1, 3]
i = [1, 4]
i = [2, 3]
i = [2, 4]
i = [3, 4]

julia> for i in subsets(1:4, Val{2}())
           @show i
       end
i = (1, 2)
i = (1, 3)
i = (1, 4)
i = (2, 3)
i = (2, 4)
i = (3, 4)

takestrict(xs, n::Int)

Like take(), an iterator that generates at most the first n elements of xs, but throws an exception if fewer than n items are encountered in xs.

julia> a = :1:2:11
1:2:11

julia> collect(takestrict(a, 3))
3-element Array{Int64,1}:
 1
 3
 5

IterTools.@ifsomething expr

If expr evaluates to nothing, equivalent to return nothing, otherwise the macro evaluates to the value of expr. Not exported, useful for implementing iterators.

julia> IterTools.@ifsomething iterate(1:2)
(1, 1)

julia> let elt, state = IterTools.@ifsomething iterate(1:2, 2); println("not reached"); end