Scrabble Stems Ruby Quiz question.

Hi all,

could someone explain the line:
(STEMS[stem] ||= {})[letter] = 1
in the code below?
This is a solution (Carlos) from the Scrabble Stems Ruby quiz.

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DICT = "/usr/share/dict/words"
CUTOFF = ARGV[0].to_i

STEMS = {}

File.open(DICT) do |f|
f.each do |word|
word.chomp!
next if word.length != 7
word.downcase!
letters = word.split(//).sort!
uniques = letters.uniq
word = letters.join
uniques.each do |letter|
stem = word.sub(letter, "")
(STEMS[stem] ||= {})[letter] = 1
end
end
end

result = STEMS.delete_if { |k,v| v.size < CUTOFF }.
sort_by { |k,v| v.size }.
reverse!.
collect! { |k,v| [k, v.size] }

result.each do |stem, combining| puts "#{stem} #{combining}" end
---------------------------------------------------------------


cheers,

--
Mark
.