Ruby: getting character[n] from each element of an array of strings, strictly with array notation

Question

Suppose I have this:

x = %w(greater yellow bandicooot)

And I want to get a specific letter of each string as a string. Of course, I can do something like this (to get the first letter):

x.map { |w| w[0] }.join  # => 'gyb'

But I'd like to know whether or not there's a way to do it using just array notation. I've tried this:

x[0][0]..x[-1][0]

Which returns, in this case, the not-so-helpful "g".."b". I could also use array notation like this in this case:

x[0][0] + x[1][0] + x[2][0]

But I'm looking for a non-case-specific solution that doesn't require iteration.

Is there a way to do this strictly with array notation, or is it necessary to do some sort of iteration? And if you can't do it with array notation, is there a better way to do it than using map and join?

Answer 1

Here's a fancy regex way to do it, if you have the word combined in a single space-delimited string:

string = "greater yellow bandicooot"
string.gsub /([^ ])[^ ]* */, '\1'
# => "gyb"

Explanation of the regex:

• ([^ ]): match group - single nonspace char
• [^ ]* *: optional sequence of nonspace chars, followed by any optional sequence of space chars.

As you can read about here: Ruby regex - gsub only captured group, when using gsub everything in the entire regex is replaced, regardless of if it's in a match group. So you need to use the special variable \1 in the gsub call (must be in a single quoted string, by the way) to refer to the first match group, that you want to use as the output.

Answer 2

I don't believe there is a way to do what you want, but you could do the following.

str = %w(greater yellow bandicooot).join(' ')
  #=> "greater yellow bandicooot"

str.gsub(/(?<=\S)./, '')
  #=> "gyb"

The regular expression matches any character that is preceded by a non-whitespace character; that is, it matches all characters other than the first character of the string and characters preceded by a whitespace character.

If one is given the string and there could be multiple spaces between words, one could write:

str.squeeze(' ').gsub(/(?<=\S)./, '')