No implicit conversion of Array into Integer (TypeError)

Question

I created a simple method that sorts characters in a string and returns true if "b" is within three (or fewer) characters after an "a" and vice-versa.

Here it is below:

def near_ab(string)
  arr = string.split("")
  a_position = arr.each_with_index.select {|i| arr[i] == "a"}
  b_position = arr.each_with_index.select {|i| arr[i] == "b"}

  if a_position - b_position <= 3      #arr[a] - arr[b] == 3
     return true
 else 
     return false
 end

end

However, after running it I get the following error:

    `[]': no implicit conversion of Array into Integer (TypeError)

Why is it giving me this error and how should I approach resolving it?

MrYoshiji · Accepted Answer · 2015-11-10 14:28:52Z

3

The method each_with_index maps the second argument as the index.

Use this instead:

arr.each_with_index.select {|element, i| arr[i] == "a"}

A better way to accomplish what you want:

def near_ab(string)
  arr = string.split("")
  a_position = arr.index('a') # Array#index returns the index of the first element that match `'a'` in this case
  b_position = arr.index('b')

  if (a_position - b_position).abs <= 3      #arr[a] - arr[b] == 3
    return true
  else 
    return false
  end
end

near_ab('hallo, ich bin Jonas!') # => returns false

(you can copy-paste this in your console to try it out)

edited Nov 10, 2015 at 14:28

answered Nov 9, 2015 at 22:13

MrYoshiji

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3 Comments

Codestudio Over a year ago

I get a new error after changing it to this: undefined method `<=' for [["a", 1]]:Array (NoMethodError)

fenton Over a year ago

That's exactly the point: The "select" statement above returns an Array. It seems the "<=" method is not defined for Array Objects and BTW I assume that you don't want to compare the Arrays. If you really want to do it like this you may add a map {|a| a[1]}after the select statement: arr.each_with_index.select {|element, i| arr[i] == "a"}.map{|a| a[1]}

fenton Over a year ago

Huh. Forget the map. I just tried and it doesn't work as well. I'd really consider to do it in a different way. This all looks quite ugly. Sorry for the misleading comment above.

the Tin Man · Accepted Answer · 2015-11-09 22:33:35Z

1

Why not use the String#index method? each_with_index needs two arguments as already said. select provides you with an Array that you can't compare by simply using <=, and that's the reason for the error.

I'd use something like:

def near_ab(string)
     a_position = string.index('a')
     b_position = string.index('b')

    (a_position - b_position).abs <= 3·
end

puts near_ab('abcde')
puts near_ab('acdeb')
puts near_ab('acdefb')

BTW, I don't see any relation to Rails in your question.

edited Nov 9, 2015 at 22:33

the Tin Man

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answered Nov 9, 2015 at 22:31

fenton

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