How to select the first n elements from Ruby array that satisfy a predicate?

Question

I want to get all items from an array, which satisfy a predicate. Once I see an element that doesn't satisfy, I should stop iterating. For example:

[1, 4, -9, 3, 6].select_only_first { |x| x > 0}

I'm expecting to get: [1, 4]

Answer 1

This is how you want :

arup@linux-wzza:~> pry
[1] pry(main)> [1, 4, -9, 3, 6].take_while { |x| x > 0}
=> [1, 4]
[2] pry(main)>

Here is the documentation :

arup@linux-wzza:~> ri Array#take_while

= Array#take_while

(from ruby site)
------------------------------------------------------------------------------
  ary.take_while { |arr| block }  -> new_ary
  ary.take_while                  -> Enumerator

------------------------------------------------------------------------------

Passes elements to the block until the block returns nil or false, then stops
iterating and returns an array of all prior elements.

If no block is given, an Enumerator is returned instead.

See also Array#drop_while

  a = [1, 2, 3, 4, 5, 0]
  a.take_while { |i| i < 3 }  #=> [1, 2]


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