Implement the accumulate
operation, which, given a collection and an
operation to perform on each element of the collection, returns a new
collection containing the result of applying that operation to each element of
the input collection.
Given the collection of numbers:
And the operation:
x => x * x
)Your code should be able to produce the collection of squares:
Check out the test suite to see the expected function signature.
Keep your hands off that collect/map/fmap/whatchamacallit functionality provided by your standard library! Solve this one yourself using other basic tools instead.
Execute the tests with:
$ elixir accumulate_test.exs
In the test suites, all but the first test have been skipped.
Once you get a test passing, you can unskip the next one by
commenting out the relevant @tag :pending
with a #
symbol.
For example:
# @tag :pending
test "shouting" do
assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end
Or, you can enable all the tests by commenting out the
ExUnit.configure
line in the test suite.
# ExUnit.configure exclude: :pending, trace: true
For more detailed information about the Elixir track, please see the help page.
Conversation with James Edward Gray II https://twitter.com/jeg2
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
if !System.get_env("EXERCISM_TEST_EXAMPLES") do
Code.load_file("accumulate.exs", __DIR__)
end
ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)
defmodule AccumulateTest do
use ExUnit.Case
test "accumulate empty list" do
assert Accumulate.accumulate([], fn n -> n * n end) == []
end
@tag :pending
test "accumulate square numbers" do
assert Accumulate.accumulate([1, 2, 3], fn n -> n * n end) == [1, 4, 9]
end
@tag :pending
test "accumulate upcased strings" do
fun = fn w -> String.upcase(w) end
assert Accumulate.accumulate(["hello", "world"], fun) == ["HELLO", "WORLD"]
end
@tag :pending
test "accumulate reversed strings" do
fun = fn w -> String.reverse(w) end
words = ~w(the quick brown fox etc)
expected = ["eht", "kciuq", "nworb", "xof", "cte"]
assert Accumulate.accumulate(words, fun) == expected
end
@tag :pending
test "nested accumulate" do
chars = ~w(a b c)
nums = ~w(1 2 3)
fun = fn c -> Accumulate.accumulate(nums, &(c <> &1)) end
expected = [["a1", "a2", "a3"], ["b1", "b2", "b3"], ["c1", "c2", "c3"]]
assert Accumulate.accumulate(chars, fun) == expected
end
end
defmodule Accumulate do
@doc """
Given a list and a function, apply the function to each list item and
replace it with the function's return value.
Returns a list.
## Examples
iex> Accumulate.accumulate([], fn(x) -> x * 2 end)
[]
iex> Accumulate.accumulate([1, 2, 3], fn(x) -> x * 2 end)
[2, 4, 6]
"""
@spec accumulate(list, (any -> any)) :: list
def accumulate(list, fun) do
do_accumulate(list, fun)
end
defp do_accumulate([], fun), do: []
defp do_accumulate([head|rest], fun) do
[fun.(head)|do_accumulate(rest, fun)]
end
end
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