Shortcut to chunk(enum, n, n).

Streams the enumerable in chunks, containing n items each, where each new chunk starts step elements into the enumerable.

step is optional and, if not passed, defaults to n, i.e. chunks do not overlap. If the final chunk does not have n elements to fill the chunk, elements are taken as necessary from pad if it was passed. If pad is passed and does not have enough elements to fill the chunk, then the chunk is returned anyway with less than n elements. If pad is not passed at all or is nil, then the partial chunk is discarded from the result.

Examples

iex> Stream.chunk([1, 2, 3, 4, 5, 6], 2) |> Enum.to_list
[[1, 2], [3, 4], [5, 6]]

iex> Stream.chunk([1, 2, 3, 4, 5, 6], 3, 2) |> Enum.to_list
[[1, 2, 3], [3, 4, 5]]

iex> Stream.chunk([1, 2, 3, 4, 5, 6], 3, 2, [7]) |> Enum.to_list
[[1, 2, 3], [3, 4, 5], [5, 6, 7]]

iex> Stream.chunk([1, 2, 3, 4, 5, 6], 3, 3, []) |> Enum.to_list
[[1, 2, 3], [4, 5, 6]]

Chunks the enum by buffering elements for which fun returns the same value and only emit them when fun returns a new value or the enum finishes.

Examples

iex> stream = Stream.chunk_by([1, 2, 2, 3, 4, 4, 6, 7, 7], &(rem(&1, 2) == 1))
iex> Enum.to_list(stream)
[[1], [2, 2], [3], [4, 4, 6], [7, 7]]

Creates a stream that enumerates each enumerable in an enumerable.

Examples

iex> stream = Stream.concat([1..3, 4..6, 7..9])
iex> Enum.to_list(stream)
[1, 2, 3, 4, 5, 6, 7, 8, 9]

Creates a stream that enumerates the first argument, followed by the second.

Examples

iex> stream = Stream.concat(1..3, 4..6)
iex> Enum.to_list(stream)
[1, 2, 3, 4, 5, 6]

iex> stream1 = Stream.cycle([1, 2, 3])
iex> stream2 = Stream.cycle([4, 5, 6])
iex> stream = Stream.concat(stream1, stream2)
iex> Enum.take(stream, 6)
[1, 2, 3, 1, 2, 3]

Creates a stream that cycles through the given enumerable, infinitely.

Examples

iex> stream = Stream.cycle([1, 2, 3])
iex> Enum.take(stream, 5)
[1, 2, 3, 1, 2]

Creates a stream that only emits elements if they are different from the last emitted element.

This function only ever needs to store the last emitted element.

Elements are compared using ===.

Examples

iex> Stream.dedup([1, 2, 3, 3, 2, 1]) |> Enum.to_list
[1, 2, 3, 2, 1]

Creates a stream that only emits elements if the result of calling fun on the element is different from the (stored) result of calling fun on the last emitted element.

Examples

iex> Stream.dedup_by([{1, :x}, {2, :y}, {2, :z}, {1, :x}], fn {x, _} -> x end) |> Enum.to_list
[{1, :x}, {2, :y}, {1, :x}]

Lazily drops the next n items from the enumerable.

If a negative n is given, it will drop the last n items from the collection. Note that the mechanism by which this is implemented will delay the emission of any item until n additional items have been emitted by the enum.

Examples

iex> stream = Stream.drop(1..10, 5)
iex> Enum.to_list(stream)
[6, 7, 8, 9, 10]

iex> stream = Stream.drop(1..10, -5)
iex> Enum.to_list(stream)
[1, 2, 3, 4, 5]

Lazily drops elements of the enumerable while the given function returns true.

Examples

iex> stream = Stream.drop_while(1..10, &(&1 <= 5))
iex> Enum.to_list(stream)
[6, 7, 8, 9, 10]

Executes the given function for each item.

Useful for adding side effects (like printing) to a stream.

Examples

iex> stream = Stream.each([1, 2, 3], fn(x) -> send self, x end)
iex> Enum.to_list(stream)
iex> receive do: (x when is_integer(x) -> x)
1
iex> receive do: (x when is_integer(x) -> x)
2
iex> receive do: (x when is_integer(x) -> x)
3

Creates a stream that filters elements according to the given function on enumeration.

Examples

iex> stream = Stream.filter([1, 2, 3], fn(x) -> rem(x, 2) == 0 end)
iex> Enum.to_list(stream)
[2]

Creates a stream that filters and then maps elements according to given functions.

Exists for symmetry with Enum.filter_map/3.

Examples

iex> stream = Stream.filter_map(1..6, fn(x) -> rem(x, 2) == 0 end, &(&1 * 2))
iex> Enum.to_list(stream)
[4, 8, 12]

Creates a stream that will apply the given function on enumeration and flatten the result.

Examples

iex> stream = Stream.flat_map([1, 2, 3], fn(x) -> [x, x * 2] end)
iex> Enum.to_list(stream)
[1, 2, 2, 4, 3, 6]

Creates a stream that emits a value after the given period n in milliseconds.

The values emitted are an increasing counter starting at 0.

Examples

iex> Stream.interval(10) |> Enum.take(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Injects the stream values into the given collectable as a side-effect.

This function is often used with run/1 since any evaluation is delayed until the stream is executed. See run/1 for an example.

Emits a sequence of values, starting with start_value. Successive values are generated by calling next_fun on the previous value.

Examples

iex> Stream.iterate(0, &(&1+1)) |> Enum.take(5)
[0, 1, 2, 3, 4]

Creates a stream that will apply the given function on enumeration.

Examples

iex> stream = Stream.map([1, 2, 3], fn(x) -> x * 2 end)
iex> Enum.to_list(stream)
[2, 4, 6]

Creates a stream that will reject elements according to the given function on enumeration.

Examples

iex> stream = Stream.reject([1, 2, 3], fn(x) -> rem(x, 2) == 0 end)
iex> Enum.to_list(stream)
[1, 3]

Returns a stream generated by calling generator_fun repeatedly.

Examples

iex> Stream.repeatedly(&:random.uniform/0) |> Enum.take(3)
[0.4435846174457203, 0.7230402056221108, 0.94581636451987]

Emits a sequence of values for the given resource.

Similar to transform/2 but the initial accumulated value is computed lazily via start_fun and executes an after_fun at the end of enumeration (both in cases of success and failure).

Successive values are generated by calling next_fun with the previous accumulator (the initial value being the result returned by start_fun) and it must return a tuple containing a list of items to be emitted and the next accumulator. The enumeration finishes if it returns {:halt, acc}.

As the name says, this function is useful to stream values from resources.

Examples

Stream.resource(fn -> File.open!("sample") end,
                fn file ->
                  case IO.read(file, :line) do
                    data when is_binary(data) -> {[data], file}
                    _ -> {:halt, file}
                  end
                end,
                fn file -> File.close(file) end)

Runs the given stream.

This is useful when a stream needs to be run, for side effects, and there is no interest in its return result.

Examples

Open up a file, replace all # by % and stream to another file without loading the whole file in memory:

stream = File.stream!("code")
|> Stream.map(&String.replace(&1, "#", "%"))
|> Stream.into(File.stream!("new"))
|> Stream.run

No computation will be done until we call one of the Enum functions or Stream.run/1.

Creates a stream that applies the given function to each element, emits the result and uses the same result as the accumulator for the next computation.

Examples

iex> stream = Stream.scan(1..5, &(&1 + &2))
iex> Enum.to_list(stream)
[1, 3, 6, 10, 15]

Creates a stream that applies the given function to each element, emits the result and uses the same result as the accumulator for the next computation. Uses the given acc as the starting value.

Examples

iex> stream = Stream.scan(1..5, 0, &(&1 + &2))
iex> Enum.to_list(stream)
[1, 3, 6, 10, 15]

Lazily takes the next count items from the enumerable and stops enumeration.

If a negative count is given, the last count values will be taken. For such, the collection is fully enumerated keeping up to 2 * count elements in memory. Once the end of the collection is reached, the last count elements will be executed. Therefore, using a negative count on an infinite collection will never return.

Examples

iex> stream = Stream.take(1..100, 5)
iex> Enum.to_list(stream)
[1, 2, 3, 4, 5]

iex> stream = Stream.take(1..100, -5)
iex> Enum.to_list(stream)
[96, 97, 98, 99, 100]

iex> stream = Stream.cycle([1, 2, 3]) |> Stream.take(5)
iex> Enum.to_list(stream)
[1, 2, 3, 1, 2]

Creates a stream that takes every nth item from the enumerable.

The first item is always included, unless nth is 0.

nth must be a non-negative integer, or FunctionClauseError will be thrown.

Examples

iex> stream = Stream.take_every(1..10, 2)
iex> Enum.to_list(stream)
[1, 3, 5, 7, 9]

iex> stream = Stream.take_every([1, 2, 3, 4, 5], 1)
iex> Enum.to_list(stream)
[1, 2, 3, 4, 5]

iex> stream = Stream.take_every(1..1000, 0)
iex> Enum.to_list(stream)
[]

Lazily takes elements of the enumerable while the given function returns true.

Examples

iex> stream = Stream.take_while(1..100, &(&1 <= 5))
iex> Enum.to_list(stream)
[1, 2, 3, 4, 5]

Creates a stream that emits a single value after n milliseconds.

The value emitted is 0.

Examples

iex> Stream.timer(10) |> Enum.to_list
[0]

Transforms an existing stream.

It expects an accumulator and a function that receives each stream item and an accumulator, and must return a tuple containing a new stream (often a list) with the new accumulator or a tuple with :halt as first element and the accumulator as second.

Note: this function is similar to Enum.flat_map_reduce/3 except the latter returns both the flat list and accumulator, while this one returns only the stream.

Examples

Stream.transform/3 is useful as it can be used as the basis to implement many of the functions defined in this module. For example, we can implement Stream.take(enum, n) as follows:

iex> enum = 1..100
iex> n = 3
iex> stream = Stream.transform(enum, 0, fn i, acc ->
...>   if acc < n, do: {[i], acc + 1}, else: {:halt, acc}
...> end)
iex> Enum.to_list(stream)
[1, 2, 3]

Transforms an existing stream with function-based start and finish.

The accumulator is only calculated when transformation starts. It also allows an after function to be given which is invoked when the stream halts or completes.

This function can be seen as a combination of Stream.resource/3 with Stream.transform/3.

Emits a sequence of values for the given accumulator.

Successive values are generated by calling next_fun with the previous accumulator and it must return a tuple with the current value and next accumulator. The enumeration finishes if it returns nil.

Examples

iex> Stream.unfold(5, fn 0 -> nil; n -> {n, n-1} end) |> Enum.to_list()
[5, 4, 3, 2, 1]

Creates a stream that only emits elements if they are unique.

Keep in mind that, in order to know if an element is unique or not, this function needs to store all unique values emitted by the stream. Therefore, if the stream is infinite, the number of items stored will grow infinitely, never being garbage collected.

Examples

iex> Stream.uniq([1, 2, 3, 3, 2, 1]) |> Enum.to_list
[1, 2, 3]

iex> Stream.uniq([{1, :x}, {2, :y}, {2, :z}, {1, :x}], fn {x, _} -> x end) |> Enum.to_list
[{1, :x}, {2, :y}]

Creates a stream where each item in the enumerable will be wrapped in a tuple alongside its index.

Examples

iex> stream = Stream.with_index([1, 2, 3])
iex> Enum.to_list(stream)
[{1, 0}, {2, 1}, {3, 2}]

Zips two collections together, lazily.

The zipping finishes as soon as any enumerable completes.

Examples

iex> concat = Stream.concat(1..3, 4..6)
iex> cycle  = Stream.cycle([:a, :b, :c])
iex> Stream.zip(concat, cycle) |> Enum.to_list
[{1, :a}, {2, :b}, {3, :c}, {4, :a}, {5, :b}, {6, :c}]