rdiff.rb

#
# Gets the reverse diff (strings that have not changed) between 2 strings
#
#
# text1 = <<END
# This is the first test.
# Not really sure what else to put here...
# END
# 
# text2 = <<END
# This is the second test.
# Not really sure what else to put here...
# Boo-Yah!
# END
# 
# rdiff( text1, text2 ) # => "This is the  test.\nNot really sure what else to put here...\n"
#
#
# @param  [String]  text1
# @param  [String]  text2
#
# @return  [String]
#
def rdiff( text1, text2 )
    
    # take care of some common cases
    return text1 if text1 == text2
    return ''    if text1 == '' || text2 == ''

    # get the words of the first text in an array
    words1 = text1.split( /\b/ )

    # get the words of the second text in an array
    words2 = text2.split( /\b/ )

    # get all the words that are different between the 2 arrays
    # math style!
    changes  = words1 - words2
    changes << words2 - words1
    changes.flatten!

    # get what hasn't changed (the rdiff, so to speak) as a string
    return ( words1 - changes ).join( '' ) 

end