Finding a character in a string using an index array

Question

I have a string to parse. I managed to use a method to find the indices of a substring. Here's the code:

indexArray = []
myString.to_enum(:scan, /(\n)/i).map do
  indexArray.push [$`.size]                                         #`
end
#indexArray = [0,2,3,4,5,6]
myString[indexArray[1]] # => no implicit conversion of Array into Integer (TypeError)

I tried using to_i, but it seems like broken logic. Any insight is appreciated. If I uncomment the second to the last line, making indexArray an array of integers, it works. I am wondering why I can get a character at an index using a basic array, but not the array derived from this method.

indexArray.push [$`.size] pushes another array onto indexArray, so you end up with something like [[0],[2],[3],[4],[5],[6]]. You probably want indexArray.push $`.size. — Stefan
– Stefan, Commented Feb 20, 2018 at 18:03
Adding an example would help quite a bit in solving this since it would allow us to see what you're trying to achieve. — neznidalibor
– neznidalibor, Commented Feb 20, 2018 at 18:33
Not at my machine right now but thank you @Stefan! This is most likely the solution — Lyres
– Lyres, Commented Feb 20, 2018 at 18:35
@Stefan can you please make an answer out of your comment so this question can be closed? — sxm1972
– sxm1972, Commented Feb 21, 2018 at 3:22

Stefan · Accepted Answer · 2018-02-21 07:06:44Z

2

First of all, you should use snake_case instead of camelCase for method names and variables. The following code is changed accordingly.

This line:

index_array.push [$`.size]

will create a new array with a single element $`.size and push that onto index_array.

You'll end up with a nested array like this: (you can inspect the array via p index_array)

index_array #=> [[0], [2], [3], [4], [5], [6]]

This can be easily fixed by just pushing $`.size (without the array):

index_array.push $`.size

Furthermore, your code can be simplified:

index_array = my_string.to_enum(:scan, /\n/).map { $`.size }

map already returns an array containing the elements returned by the given block.
the capture group around \n is not used and therefore not needed.
the i flag is superfluous because there's only one \n.

answered Feb 21, 2018 at 7:06

Stefan

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