How do I apply a function to an array and form two separate arrays?

问题

I'm using Ruby 2.4. I have an array with string data elements, that look like

["a word1 word2", "b eff", "a idaho orange", "new old shoe", "b mars", ...]

I want to form two arrays from the above, applying a function (.split(/^(a|b)[[:space]]*/i) to each element of the array. However, I can't figure out how to form two separate arrays. The following

arr.map{ |x| x.split(/^(a|b)[[:space]]*/i) }

only results in a single array and has a blank element in front of each element. Ideally, I'd like the output to be two arrays like

["a", "b", "a", "", "b", ...]
["word1 word2", "eff", "idaho orange", "new old shoe", "mars", ...]

回答1:

Try this

arr.map { |x| a, b, c = x.partition(/^[ab]\s+/); [b.strip, a + c] }.transpose

How does this work?

• partition splits a string into before-match, match and post-match
• b.strip is the match without trailing whitespace
• a + c is either the full string (if there was no match the full string is in before-match) or the post-match
• [..., ...] creates a tuple, hence creating an array of tuple
• transpose switches the rows and columns of a 2D array

回答2:

Regex only

This is the shortest I could find :

a1, a2 = arr.map{ |x| x.match(/((?:^[ab](?= ))?) *(.*)/).captures}.transpose

This example now works with "activity" or "ball". It checks if a space follows directly after a or b at the beginning of the string.

Split and logic

Another variant would be :

a1, a2 = arr.map do |x|
  parts = x.split(/(?<=^a|^b) +/)
  parts.unshift('') if parts.size == 1
  parts
end.transpose

来源：https://stackoverflow.com/questions/41795017/how-do-i-apply-a-function-to-an-array-and-form-two-separate-arrays