ruby,dictionary , Why is reject not rejecting?

Question:

Tag: ruby,dictionary

This code is my initial stab at the Hamming Distance problem on Exercism.io, but it fails the case when string a is longer than string b, and I'm trying to understand why.

def self.compute(a, b)
a.split('').reject.with_index { |c, i| c == b[i] }.size
end


I got around the problem by trimming the first string...

def self.compute(a, b)
a[0...b.size].split('').reject.with_index { |c, i| c == b[i] }.size
end


...but I don't understand why reject is including the extra characters. When I check the comparisons, they seem to be coming up false, as I would expect, yet are still included in the result.

Can anyone tell me why?

I don't understand why reject is including the extra characters. When I check the comparisons, they seem to be coming up false

Correct. And when you're rejecting, false means "accept" - the opposite of reject.

The problem is merely that you're not grasping what "reject" means. When you're up against a question like this, debug. In this case, the way to do that is to eliminate the superfluous material and focus on the thing that's confusing you. Remove the size call and just look at the results of the reject call:

def compute(a, b)
a.split('').reject.with_index { |c, i| c == b[i] }
end
result = compute("hey", "ha")
puts result


The output is "e" and "y". And this makes sense:

• On the first pass, "h" == "h" and is rejected.

• On the second pass, "e" != "a" and is accepted.

• On the third pass, "y" has nothing to compare it with, so it cannot succeed; thus we fail to reject — and so the "y" is accepted. That's what you're asking about.

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