Find and print lines in a file exactly matching string or regexp (Ruby)

Question

In ruby 1.9.3, I'm trying to write a program that will find all words with n number of characters taken from an arbitrary set of characters. So for instance, if I'm given the characters [ b, a, h, s, v, i, e, y, k, s, a ] and n = 5, I need to find all 5-letter words that can be made using only those characters. Using the 2of4brif.txt word list from http://wordlist.sourceforge.net/ (to include British words and spellings, too), I have attempted the following code:

a = %w[b a h s v i e y k s a]
a.permutation(5).map(&:join).each do |x|
  File.open('2of4brif.txt').each_line do |line|
    puts line if line.match(/^[#{x}]+$/)
  end
end

This does nothing (no error message, no output, as if frozen). I have also attempted variations based on the following threads:

What's the best way to search for a string in a file?

Ruby find string in file and print result

How to search for exact matching string in a text file using Ruby?

Finding lines in a text file matching a regular expression

Match a content with regexp in a file?

How to open a file and search for a word?

Every variation I have tried has resulted in either:

1) Freezing;

2) Printing all words from the list that contain the 5-character permutations (I assume that's what it's doing; I didn't go through and check all of the thousands of printed words); or

3) Printing all 5-character permutations found within words in the list (again, I assume that's what it's doing).

Again, I'm not looking for words that contain the 5-character permutations, I'm looking for 5-character permutations that are complete words in and of themselves, so a line in the text file should only be printed if it is a perfect match with a permutation.

What am I doing wrong? Thanks in advance!

Answer 1

You’re not really using regular expressions here. Your program is very inefficient, not only because you’re re-opening the file for each single permutation as has been pointed out (and there are 55k of them!); but above all because all you want to do is

/^[bahsvieyksa]{5}$/

for each line of the file.

I would thus suggest:

File.open('2of4brif.txt').each_line do |line|
  puts line if line.match(/^[bahsvieyksa]{5}$/)
end

as a much more efficient alternative

Answer 2

This works for me using the english.0 file on that page (sorry, I couldn't find the specific file you mentioned):

a = %w[b a h s v i e y k s a l d n]
dict = {}
a.permutation(5).each do |p|
  dict[p.join('')] = true
end

File.open('english.0').each_line do |line|
  line.chomp!.downcase!
  puts line if dict[line]
end

The structure should be pretty clear - I build the dictionary of permutations up front in one giant hash (you may need to revisit this depending on input sizes, but memory is cheap these days), and then I used the fact that the input was "one word per line" to simply key into that hash.

Also note, in my version, I read through the file only once. In yours you scan the file once per permutation, and there are thousands of permutations.