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Base.Iterators.Stateful
— Type
Stateful(itr)
There are several different ways to think about this iterator wrapper:
- It provides a mutable wrapper around an iterator and its iteration state.
- It turns an iterator-like abstraction into a
Channel
-like abstraction. - It’s an iterator that mutates to become its own rest iterator whenever an item is produced.
Stateful
provides the regular iterator interface. Like other mutable iterators (e.g. Channel
), if iteration is stopped early (e.g. by a break
in a for
loop), iteration can be resumed from the same spot by continuing to iterate over the same iterator object (in contrast, an immutable iterator would restart from the beginning).
Examples
julia> a = Iterators.Stateful("abcdef");
julia> isempty(a)
false
julia> popfirst!(a)
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)
julia> collect(Iterators.take(a, 3))
3-element Array{Char,1}:
'b'
'c'
'd'
julia> collect(a)
2-element Array{Char,1}:
'e'
'f'
julia> a = Iterators.Stateful([1,1,1,2,3,4]);
julia> for x in a; x == 1 || break; end
julia> Base.peek(a)
3
julia> sum(a) # Sum the remaining elements
7
Base.Iterators.zip
— Function
zip(iters...)
Run multiple iterators at the same time, until any of them is exhausted. The value type of the zip
iterator is a tuple of values of its subiterators.
Note: zip
orders the calls to its subiterators in such a way that stateful iterators will not advance when another iterator finishes in the current iteration.
Examples
julia> a = 1:5
1:5
julia> b = ["e","d","b","c","a"]
5-element Array{String,1}:
"e"
"d"
"b"
"c"
"a"
julia> c = zip(a,b)
Base.Iterators.Zip{Tuple{UnitRange{Int64},Array{String,1}}}((1:5, ["e", "d", "b", "c", "a"]))
julia> length(c)
5
julia> first(c)
(1, "e")
Base.Iterators.enumerate
— Function
enumerate(iter)
An iterator that yields (i, x)
where i
is a counter starting at 1, and x
is the i
th value from the given iterator. It’s useful when you need not only the values x
over which you are iterating, but also the number of iterations so far. Note that i
may not be valid for indexing iter
; it’s also possible that x != iter[i]
, if iter
has indices that do not start at 1. See the pairs(IndexLinear(), iter)
method if you want to ensure that i
is an index.
Examples
julia> a = ["a", "b", "c"];
julia> for (index, value) in enumerate(a)
println("$index $value")
end
1 a
2 b
3 c
Base.Iterators.rest
— Function
rest(iter, state)
An iterator that yields the same elements as iter
, but starting at the given state
.
Examples
julia> collect(Iterators.rest([1,2,3,4], 2))
3-element Array{Int64,1}:
2
3
4
Base.Iterators.countfrom
— Function
countfrom(start=1, step=1)
An iterator that counts forever, starting at start
and incrementing by step
.
Examples
julia> for v in Iterators.countfrom(5, 2)
v > 10 && break
println(v)
end
5
7
9
Base.Iterators.take
— Function
take(iter, n)
An iterator that generates at most the first n
elements of iter
.
Examples
julia> a = 1:2:11
1:2:11
julia> collect(a)
6-element Array{Int64,1}:
1
3
5
7
9
11
julia> collect(Iterators.take(a,3))
3-element Array{Int64,1}:
1
3
5
Base.Iterators.drop
— Function
drop(iter, n)
An iterator that generates all but the first n
elements of iter
.
Examples
julia> a = 1:2:11
1:2:11
julia> collect(a)
6-element Array{Int64,1}:
1
3
5
7
9
11
julia> collect(Iterators.drop(a,4))
2-element Array{Int64,1}:
9
11
Base.Iterators.cycle
— Function
cycle(iter)
An iterator that cycles through iter
forever. If iter
is empty, so is cycle(iter)
.
Examples
julia> for (i, v) in enumerate(Iterators.cycle("hello"))
print(v)
i > 10 && break
end
hellohelloh
Base.Iterators.repeated
— Function
repeated(x[, n::Int])
An iterator that generates the value x
forever. If n
is specified, generates x
that many times (equivalent to take(repeated(x), n)
).
Examples
julia> a = Iterators.repeated([1 2], 4);
julia> collect(a)
4-element Array{Array{Int64,2},1}:
[1 2]
[1 2]
[1 2]
[1 2]
Base.Iterators.product
— Function
product(iters...)
Return an iterator over the product of several iterators. Each generated element is a tuple whose i
th element comes from the i
th argument iterator. The first iterator changes the fastest.
Examples
julia> collect(Iterators.product(1:2, 3:5))
2×3 Array{Tuple{Int64,Int64},2}:
(1, 3) (1, 4) (1, 5)
(2, 3) (2, 4) (2, 5)
Base.Iterators.flatten
— Function
flatten(iter)
Given an iterator that yields iterators, return an iterator that yields the elements of those iterators. Put differently, the elements of the argument iterator are concatenated.
Examples
julia> collect(Iterators.flatten((1:2, 8:9)))
4-element Array{Int64,1}:
1
2
8
9
Base.Iterators.partition
— Function
partition(collection, n)
Iterate over a collection n
elements at a time.
Examples
julia> collect(Iterators.partition([1,2,3,4,5], 2))
3-element Array{Array{Int64,1},1}:
[1, 2]
[3, 4]
[5]
Base.Iterators.filter
— Function
Iterators.filter(flt, itr)
Given a predicate function flt
and an iterable object itr
, return an iterable object which upon iteration yields the elements x
of itr
that satisfy flt(x)
. The order of the original iterator is preserved.
This function is lazy; that is, it is guaranteed to return in $Θ(1)$ time and use $Θ(1)$ additional space, and flt
will not be called by an invocation of filter
. Calls to flt
will be made when iterating over the returned iterable object. These calls are not cached and repeated calls will be made when reiterating.
See Base.filter
for an eager implementation of filtering for arrays.
Examples
julia> f = Iterators.filter(isodd, [1, 2, 3, 4, 5])
Base.Iterators.Filter{typeof(isodd),Array{Int64,1}}(isodd, [1, 2, 3, 4, 5])
julia> foreach(println, f)
1
3
5
Base.Iterators.reverse
— Function
Iterators.reverse(itr)
Given an iterator itr
, then reverse(itr)
is an iterator over the same collection but in the reverse order.
This iterator is “lazy” in that it does not make a copy of the collection in order to reverse it; see Base.reverse
for an eager implementation.
Not all iterator types T
support reverse-order iteration. If T
doesn’t, then iterating over Iterators.reverse(itr::T)
will throw a MethodError
because of the missing iterate
methods for Iterators.Reverse{T}
. (To implement these methods, the original iterator itr::T
can be obtained from r = Iterators.reverse(itr)
by r.itr
.)
Examples
julia> foreach(println, Iterators.reverse(1:5))
5
4
3
2
1