What's the fastest way to check if a word from one string is in another string?

Question

I have a string of words; let's call them bad:

bad = "foo bar baz"

I can keep this string as a whitespace separated string, or as a list:

bad = bad.split(" ");

If I have another string, like so:

str = "This is my first foo string"

What's the fasted way to check if any word from the bad string is within my comparison string, and what's the fastest way to remove said word if it's found?

#Find if a word is there
bad.split(" ").each do |word|
  found = str.include?(word)
end

#Remove the word
bad.split(" ").each do |word|
  str.gsub!(/#{word}/, "")
end

Answer 1

If the list of bad words gets huge, a hash is a lot faster:

    require 'benchmark'

    bad = ('aaa'..'zzz').to_a    # 17576 words
    str= "What's the fasted way to check if any word from the bad string is within my "
    str += "comparison string, and what's the fastest way to remove said word if it's "
    str += "found" 
    str *= 10

    badex = /\b(#{bad.join('|')})\b/i

    bad_hash = {}
    bad.each{|w| bad_hash[w] = true}

    n = 10
    Benchmark.bm(10) do |x|

      x.report('regex:') {n.times do 
        str.gsub(badex,'').squeeze(' ')
      end}

      x.report('hash:') {n.times do
        str.gsub(/\b\w+\b/){|word| bad_hash[word] ? '': word}.squeeze(' ')
      end}

    end
                user     system      total        real
regex:     10.485000   0.000000  10.485000 ( 13.312500)
hash:       0.000000   0.000000   0.000000 (  0.000000)

Answer 2

bad = "foo bar baz"

=> "foo bar baz"

str = "This is my first foo string"

=> "This is my first foo string"

(str.split(' ') - bad.split(' ')).join(' ')

=> "This is my first string"