How do I scan every element of an array except one index?

Question

I'm using Ruby 2.4. How do I scan every element of an array for a condition except one index in the array? I tried this

arr.except(2).any? {|str| str.eql?("b")}

But got the following error:

NoMethodError: undefined method `except' for ["a", "b", "c"]:Array

but evidently what I read online about "except" is greatly exaggerated.

What exactly did you read about `except`, and where? Ruby arrays have no such method. Also, calling `.eql?` on strings is not terribly idiomatic; you can just do `str == "b"`. — Mark Reed, Mar 02 '17 at 20:28
I found a post where someone defines such a method themselves, but even there it is based on the value of the element, not its index. — Mark Reed, Mar 02 '17 at 20:33
[is this the one? :)](https://coderwall.com/p/skzsoa/ruby-array-except) — Andrey Deineko, Mar 02 '17 at 20:34
@MarkReed wouldn't `eql` be idiomatic to ruby considering most languages use some form of `==`? It also reads more like natural language. — max pleaner, Mar 02 '17 at 20:48
`.eql?` is certainly Ruby, but using it to compare Strings is not typical in Ruby code - which is what I meant by "idiomatic Ruby". *As long as both objects being compared are Strings*, `eql?` and `==` and `===` all perform the same comparison. And since far more languages use `==` for comparison than any of the others, it's usually considered the most natural choice. — Mark Reed, Mar 02 '17 at 21:05

Andrey Deineko · Accepted Answer · 2017-03-02T20:46:34.910

4

arr.reject.with_index { |_el, index| index == 2 }.any? { |str| str.eql?("b") }

Explanation:

arr = [0, 1, 2, 3, 4, 5]
arr.reject.with_index { |_el, index| index == 2 }
#=> [0, 1, 3, 4, 5]

Shortening what you are doing:

arr.reject.with_index { |_el, index| index == 2 }.grep(/b/).any?
#=> true

Following the @Cary's comment, another option would be:

arr.each_with_index.any? { |str, i| i != 2 && str.eql?("b") }

edited Mar 02 '17 at 20:46

answered Mar 02 '17 at 20:27

Andrey Deineko

1 Answers1