Question

I am wondering how one would search through an array of hashes and return a value based on a search string. For example, @contacts contains the hash elements: :full_name, :city, and :email. The variable @contacts (I guess it would be an array) contains three entries (perhaps rows). Below is the code I have so far to conduct a search based on :city value. However it’s not working. Can anyone give me an idea what’s going on?

def search string
  @contacts.map {|hash| hash[:city] == string}
end

Answer 1

You should use select instead of map:

def search string
  @contacts.select { |hash| hash[:city] == string }
end

In your code you tried to map (or transform) your array using a block, which yields boolean values. map takes a block and invokes the block for each element of self, constructing a new array containing elements returned by the block. As the result, you got an array of booleans.

select works similar. It takes a block and iterates over the array as well, but instead of transforming the source array it returns an array containing elements for which the block returns true. So it’s a selection (or filtering) method.

In order to understand the difference between these two methods it’s useful to see their example definitions:

class Array
  def my_map
    [].tap do |result|
      self.each do |item|
        result << (yield item)
      end
    end
  end

  def my_select
    [].tap do |result|
      self.each do |item|
        result << item if yield item
      end
    end
  end
end

Example usage:

irb(main):007:0> [1,2,3].my_map { |x| x + 1 }
[2, 3, 4]
irb(main):008:0> [1,2,3].my_select { |x| x % 2 == 1 }
[1, 3]
irb(main):009:0>