Common functional iterator patterns.
Iterators.jl has been deprecated in favour of IterTools.jl. Please update your package dependencies: Iterators 0.3.1 maps to IterTools 0.1.0.
See #104 for more information.
Install this package with Pkg.add("Iterators")

takestrict(xs, n)
Equivalent to
take
, but will throw an exception if fewer thann
items are encountered inxs
. 
repeatedly(f, [n])
Call a function
n
times, or infinitely ifn
is omitted.Example:
for t in repeatedly(time_ns, 3) @show t end
t = 0x0000592ff83caf87 t = 0x0000592ff83d8cf4 t = 0x0000592ff83dd11e

chain(xs...)
Iterate through any number of iterators in sequence.
Example:
for i in chain(1:3, ['a', 'b', 'c']) @show i end
i = 1 i = 2 i = 3 i = 'a' i = 'b' i = 'c'

product(xs...)
Iterate over all combinations in the cartesian product of the inputs.
Example:
for p in product(1:3,1:2) @show p end
yields
p = (1,1) p = (2,1) p = (3,1) p = (1,2) p = (2,2) p = (3,2)

distinct(xs)
Iterate through values skipping over those already encountered.
Example:
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

nth(xs, n)
Return the n'th element of
xs
. Mostly useful for non indexable collections.Example:
nth(1:3, 3)
3

takenth(xs, n)
Iterate through every n'th element of
xs
Example:
collect(takenth(5:15,3))
3element Array{Int32,1}: 7 10 13

partition(xs, n, [step])
Group values into
n
tuples.Example:
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 bystep
values.Example:
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)

groupby(f, xs)
Group consecutive values that share the same result of applying
f
.Example:
for i in groupby(x > x[1], ["face", "foo", "bar", "book", "baz", "zzz"]) @show i end
i = ASCIIString["face","foo"] i = ASCIIString["bar","book","baz"] i = ASCIIString["zzz"]

imap(f, xs1, [xs2, ...])
Iterate over values of a function applied to successive values from one or more iterators.
Example:
for i in imap(+, [1,2,3], [4,5,6]) @show i end
i = 5 i = 7 i = 9

subsets(xs)
Iterate over every subset of a collection
xs
.Example:
for i in subsets([1,2,3]) @show i end
i = [] i = [1] i = [2] i = [1,2] i = [3] i = [1,3] i = [2,3] i = [1,2,3]

subsets(xs, k)
Iterate over every subset of size
k
from a collectionxs
.Example:
for i in subsets([1,2,3],2) @show i end
i = [1,2] i = [1,3] i = [2,3]

peekiter(xs)
Add possibility to peek head element of an iterator without updating the state.
Example:
it = peekiter(["face", "foo", "bar", "book", "baz", "zzz"]) s = start(it) @show peek(it, s) @show peek(it, s) x, s = next(it, s) @show x @show peek(it, s)
peek(it,s) = Nullable("face") peek(it,s) = Nullable("face") # no change x = "face" peek(it,s) = Nullable("foo")

ncycle(xs,n)
Cycles through an iterator
n
timesExample:
for i in ncycle(1:3, 2) @show i end
i = 1 i = 2 i = 3 i = 1 i = 2 i = 3

iterate(f, x)
Iterate over successive applications of
f
, as inf(x), f(f(x)), f(f(f(x))), ...
.Example:
for i in take(iterate(x > 2x, 1), 5) @show i end
i = 1 i = 2 i = 4 i = 8 i = 16
Using functional iterators is powerful and concise, but may incur in some
overhead, and manually inlining the operations can typically improve
performance in critical parts of the code. The @itr
macro is provided to do
that automatically in some cases. Its usage is trivial: for example, given this code:
for (x,y) in zip(a,b)
@show x,y
end
the automatically inlined version can be obtained by simply doing:
@itr for (x,y) in zip(a,b)
@show x,y
end
This typically results in faster code, but its applicability has limitations:
 it only works with
for
loops;  if multiple nested iterators are used, only the outermost is affected by the transformation;
 explicit expressions are required (i.e. when a
Tuple
is expected, an explicit tuple must be provided, a tuple variable won't be accepted);  splicing is not supported;
 multidimensional loops (i.e. expressions such as
for x in a, y in b
) are not supported
The @itr
macro can be used with the following supported iterators:
 zip
 enumerate
 take
 takestrict
 drop
 chain