How many objects have the same attribute value?

Question

I have an array of objects with top and left attributes like this:

[{top: 30, left: 20}, {top:50, left:10}, {..}]

I am trying to find how many objects have the approximate same top value. In this case:

[{top: 10, left: 20}, {top:10, left:10}, {top: 10, left: 123},
{top:500, left:10}, {top:2, left: 50}, {top:2, left:400}]

the method would return 5 because there are three objects that have 10 as top value and two objects that have 2 as top value. If there is an object that doesn't share its top value with anything else, it is not taken into account. I am not looking for exact values, but with a flexibility of a 10% of difference on the values so that {top:10, left:20} and {top:10.13, left:20} would be considered as having the same top. So far, I have this:

myarr.group_by { |x| x[:top] }.map { |k,v| [k, v.length] }.to_h

but this would not take into account this margin error. I am not sure how I would change it in order to do so.

Answer 1

Depending on how you want to express "similar", you could do something like this:

def count_similar(a, lower_bound, upper_bound)
  a.count { |h| h[:top] >= lower_bound && h[:top] <= upper_bound }
end

a = [{top: 10, left: 20}, {top:10, left:10}, {top: 10, left: 123},
     {top:500, left:10} , {top:2, left: 50}, {top:2, left:400}]

count_similar(a, 1, 19) #=> 5