How to diff two arrays in ruby and get just the values that are different between the two arrays.

array_diff.rb

first_hdr = ["hello", "world"]
second_hdr = ["hello", "world", "!"]
new_columns = second_hdr - first_hdr # changed the code to use the way Morgan found, seems more ruby to me ;)

# output
# new_columns => ["!"]

# can also use reject! and that will reject on the second_hdr so then it would be
# second_hdr => ["!"]

# Happy Rubying =)

# Also see Morgan's comments below. I actully like his method better. He is a much beter developer than me and thinks of even 
# better ways of doing things.

For the first use case (the one without "reject!") you can also do:

second_hdr - first_hdr

e.g.:

new_columns = second_hdr - first_hdr

# output
# new_columns => ["!"]

# you can also use second_hdr -= first_hdr as an equivalent to your reject! example
second_hdr -= first_hdr

# output
# second_hdr => ["!"]

Nice I like that way better.