Question

I’m using ruby 1.9.3 and I need to compare two hashes that have different key formats. For example, I want the equality of the following two hashes to be the true:

hash_1 = {:date => 2011-11-01, :value => 12}
hash_2 = {"date" => 2011-11-01, "value" => 12}

Any ideas on how these two hashes can be compared in one line of code?

Answer 1

Stringify the keys on the hash that has symbols:

 > hash_1.stringify_keys
=> {"date"=>"2011-11-01", "value"=>12} 

Then compare. So, your answer, in one line, is:

 > hash_1.stringify_keys == hash_2    
=> true

You could also do it the other way around, symbolizing the string keys in hash_2 instead of stringifying them in hash_1:

 > hash_1 == hash_2.symbolize_keys
=> true

If you want the stringification/symbolization to be a permanent change, use the version with the bang !: stringify_keys! or symbolize_keys! respectively

 > hash_1.stringify_keys!                # <- Permanently changes the keys in hash_1 into Strings
=> {"date"=>"2011-11-01", "value"=>12}   #    as opposed to temporarily changing them for comparison

Ref: http://as.rubyonrails.org/classes/HashWithIndifferentAccess.html

Also, I’m guessing you meant to put quotes around the dates…

:date => "2011-11-01"

…or, explicitly instantiate them as Date objects?

:date => Date.new("2011-11-01")

The way you have the date written now sets :date to 2011-11-01 These are currently being interpreted as series of integers with subtraction in between them.

That is:

 > date = 2011-11-01
=> 1999                # <- integer value of 2011, minus 11, minus 1