Selecting indexed item froman element in a two dimensional array in Ruby

Question

I am unsure how to select the second item from each array in a two-dimensional array given a condition on the first. Here is a similar example to what I am trying to accomplish:

If you have a 2-dimensional array in Ruby, [[1,'a'],[2,'b'],[3,'c'],[4,'d']], how could you create an array with only the letters that are in an array with an even number? (Assuming each sub-array has the same format: [number, letter])

Although this code does not work, I assumed a solution would be similar to:

array1 = [[1,'a'],[2,'b'],[3,'c'],[4,'d']]
array2 = array1.each do |num, letter|
  if num.even?
    return letter
  end
end

I want the value of array2 after running this to be ['b', 'd'].

pazinjanka · Accepted Answer · 2020-06-09 06:35:06Z

2

You can do that with collect and compact combination:

array1.collect { |num, letter| letter if num.even? }.compact

First, you collect all the results of the if statement, then you compact to remove all the nil occurrences.

answered Jun 9, 2020 at 6:35

pazinjanka

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1 Comment

johndisk Over a year ago

Does this alter the original array as well? --edit: I have tested it and it does not; thank you!

Cary Swoveland · Accepted Answer · 2020-06-09 06:53:26Z

1

arr.each_with_object([]) { |(n,s),arr| arr << s if n.even? }
  #=> ["b", "d"]

I would have added explanatory comments but could not find anything that required explanation.

answered Jun 9, 2020 at 6:53

Cary Swoveland

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Comments

Sebastián Palma · Accepted Answer · 2020-06-09 06:55:06Z

1

For verbosity, select every array where the number is even, and then map their last element:

array1.select { |num, _| num.even? }.map(&:last)
# ["b", "d"]

answered Jun 9, 2020 at 6:55

Sebastián Palma

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