regex - How to match full words and not substrings in Ruby

Question

This is my code

stopwordlist = "a|an|all"
File.open('0_9.txt').each do |line|
line.downcase!
line.gsub!( /#{stopwordlist}/,'')
File.open('0_9_2.txt', 'w') { |f| f.write(line) }
end

I wanted to remove words - a,an and all But, instead it matches substrings also and removes them

For an example input -

Bromwell High is a cartoon comedy. It ran at the same time as some other programs about school life

I get the output -

bromwell high is  cartoon comedy. it r t the same time s some other programs bout school life

As you can see, it matched the substring.

How do I make it just match the word and not substrings ?

Answer 1

The | operator in regex takes the widest scope possible. Your original regex matches either a or an or all.

Change the whole regex to:

/(?:#{stopwordlist})/

or change stopwordlist into a regex instead of a string.

stopwordlist = /a|an|all/

Even better, you may want to use Regexp.union.