Using a hash to count incrementally

   By chris on June 1st 2007 in /dev/ruby | 840 views

A hash is great for keeping track of counts of things if you we already know what those things are, but how to add a new thing without a bunch of cumbersome code? Use fetch():

PLAIN TEXT
RUBY:
  1. count[item] = count.fetch(item, 0) + 1

If item already exists then it will add 1 to it. If item doesn't exist, it'll initialize it with a value of 0 and then add 1 to it.

2 Responses to “Using a hash to count incrementally”

  1. sam responded on 01 Jun 2007 at 10:37 pm #

    hash also has constructors that allow you to set the default value for non-existent hash items

    irb(main):001:0> h = Hash.new(0)
    => {}
    irb(main):002:0> h["this"] += 1
    => 1
    irb(main):003:0> h["this"] += 1
    => 2
    irb(main):004:0> h["this"]
    => 2

  2. Chris responded on 02 Jun 2007 at 2:00 am #

    Interesting. Cleaner and shorter, I like that.

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