Question

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How to count duplicates in Ruby Arrays
Ruby: Compare 2 arrays for matches, and count the number of match instances

I am starting to using ruby language. Suppose I have two arrays:

a=["A", "B", "C", "D"]
b=["C", "A", "X", "Y", "F"]

I would like to count the number of duplicated elements of the two arrays. To achieve this, the idea I came up with is like following:

nr_of_duplicates = (a- (a - b)).size

Is there a better way to achieve this?

Answer 1

There is already a method defined in Array class for this called ‘&‘:

ary & other_ary → new_ary

Set Intersection—Returns a new array containing elements common to the two arrays, with no duplicates.

   [ 1, 1, 3, 5 ] & [ 1, 2, 3 ]   #=> [ 1, 3 ]