Good notes posted by LacKac

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August 17, 2008
6 thanks

Re: Convert an Array of Arrays to a Hash using inject

If you’re sure you have a two-level array (no other arrays inside the pairs) and exactly two items in each pair, then it’s faster and shorter to use this:

array = [['A', 'a'], ['B', 'b'], ['C', 'c']]
hash = Hash[*array.flatten]

For more than two-level deep arrays this will give the wrong result or even an error (for some inputs).

array = [['A', 'a'], ['B', 'b'], ['C', ['a', 'b', 'c']]]
hash = Hash[*array.flatten]
# => {"A"=>"a", "B"=>"b", "C"=>"a", "b"=>"c"}

But if you’re running Ruby 1.8.7 or greater you can pass an argument to Array#flatten and have it flatten only one level deep:

# on Ruby 1.8.7+
hash = Hash[*array.flatten(1)]
# => {"A"=>"a", "B"=>"b", "C"=>["a", "b", "c"]}
August 13, 2008
7 thanks

Re: Helper method taking a block

The same using the ActionView::Helpers::TagHelper#content_tag and ActionView::Helpers::CaptureHelper#capture methods:

def render_tree(collection, &block)
      collection.collect { |item|
        content_tag(:li, capture(item, &block))

The benefit is that it’s easier to improve with html attributes (just add a hash of options to the content_tag call) and it makes just one call to concat (which probably makes it faster).