RUBY: Set variable to array element, regex thinks its an array

Question

I am trying to regex a character from a string that was assigned from an element of a scan result. I am trying to use match and it is complaining that the variable is an array. I am confused as to why "trash" is being seen as an array.

test = 'class="date">B=oddTu Q='
array = test.scan(/([A-Z])=/)
puts array
trash = array.last
trash.to_s
puts trash
if /Q/.match(trash)
  puts $1
end

And this is the results I'm seeing

C:\Ruby>scratch.rb
class="date">B=oddTu Q=
B
Q
Q
C:/Ruby/scratch.rb:14:in match: can't convert Array to String (TypeError)
        from C:/Ruby/scratch.rb:14:in `<main>'

EDIT: scan returns an array of array, so by doing trash = array.last, trash then gets taken down one level to 1 array. Doing trash = trash[0] then takes it down to a string.

array is an array of arrays, so trash is actually an array. Use p trash to dump the variable and you'll see — Lee Jarvis
– Lee Jarvis, Commented Dec 13, 2012 at 12:57

Boris Strandjev · Accepted Answer · 2012-12-13 12:54:40Z

2

The problem is that trash is an array (of single element "Q"). You see it when you serialize.

See those two lines taken from my irb:

test.scan(/([A-Z])=/)
=> [["B"], ["Q"]]

The scan is returning array of arrays - for each match a value for each group.

You can not do matching on an array.

answered Dec 13, 2012 at 12:54

Boris Strandjev

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Andrew Haines · Accepted Answer · 2012-12-13 14:33:40Z

1

As Boris points out, you're getting an array of arrays. It's because you have a group in your regex (a parenthesised expression). If you had several such groups, they would each correspond to an element in the returned arrays:

test.scan(/([A-Z])(=)/)
# => [["B", "="], ["Q", "="]]

In your case there's a few ways around this. You could simply flatten the array:

test.scan(/([A-Z])=/).flatten
# => ["B", "Q"]

or you could use a positive lookahead instead of grouping the bit you're interested in:

test.scan(/[A-Z](?==)/)
# => ["B", "Q"]

Unfortunately, since the bit you're not interested in is the = sign, it looks a bit weird with the lookahead syntax (?=pattern), so the flatten option might be clearer.

answered Dec 13, 2012 at 14:33

Andrew Haines

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