When you want to know something like a Venn diagram
p (array1 | array2).size p (array1 & array2).size p (array1 - (array1 & array2)).size p (array2 - (array1 & array2)).size
But I just don't know how to do it smarter.
Is there any recommended method?
Also, is there a recommended method even when there are two or more arrays?
For the time being,
(a - (a & b)).size is redundant to find "the number of elements contained in set
a but not in set
(a - b).size
You can find it just by saying.