# Strain

Implement the `keep` and `discard` operation on collections. Given a collection
and a predicate on the collection's elements, `keep` returns a new collection
containing those elements where the predicate is true, while `discard` returns
a new collection containing those elements where the predicate is false.

For example, given the collection of numbers:

- 1, 2, 3, 4, 5

And the predicate:

- is the number even?

Then your keep operation should produce:

- 2, 4

While your discard operation should produce:

- 1, 3, 5

Note that the union of keep and discard is all the elements.

The functions may be called `keep` and `discard`, or they may need different
names in order to not clash with existing functions or concepts in your
language.

## Restrictions

Keep your hands off that filter/reject/whatchamacallit functionality
provided by your standard library!  Solve this one yourself using other
basic tools instead.

* * * *

For installation and learning resources, refer to the
[exercism help page](http://exercism.io/languages/ruby).

For running the tests provided, you will need the Minitest gem. Open a
terminal window and run the following command to install minitest:

    gem install minitest

If you would like color output, you can `require 'minitest/pride'` in
the test file, or note the alternative instruction, below, for running
the test file.

Run the tests from the exercise directory using the following command:

    ruby strain_test.rb

To include color from the command line:

    ruby -r minitest/pride strain_test.rb


## Source

Conversation with James Edward Gray II [https://twitter.com/jeg2](https://twitter.com/jeg2)

## Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.