How to group by count in array without using loop

Question

arr = [1,2,1,3,5,2,4] 

How can I count the array by group value with sorting? I need the following output:

x[1] = 2   x[2] = 2   x[3] = 1   x[4] = 1   x[5] = 1 

Answer 1

x = arr.inject(Hash.new(0)) { |h, e| h[e] += 1 ; h } 

Answer 2

Only available under ruby 1.9

Basically the same as Michael's answer, but a slightly shorter way:

x = arr.each_with_object(Hash.new(0)) {|e, h| h[e] += 1} 

In similar situations,

• When the starting element is a mutable object such as an Array, Hash, String, you can use each_with_object, as in the case above.

• When the starting element is an immutable object such as Numeric, you have to use inject as below.

  sum = (1..10).inject(0) {|sum, n| sum + n} # => 55