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24 lines
558 B
Markdown
24 lines
558 B
Markdown
# Pass A Block To Count
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Ruby's [`Enumerable`](http://ruby-doc.org/core-2.2.3/Enumerable.html) module
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comes with the method `#count` for determining how many items are in an
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array or hash.
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```ruby
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> [1,2,3].count
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=> 3
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> {a: 1, b: 2}.count
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=> 2
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```
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The `#count` method has a trick up its sleeve though. It can take a block
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with a predicate that returns `true` or `false`. It essentially acts like
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`#select` returning the count rather than the array subset itself.
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```ruby
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> [1,2,3].count { |x| x.odd? }
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=> 2
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> {a: 1, b: 2}.count { |(x,y)| y < 0 }
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=> 0
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```
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