I've been hard at work on More Things Need To this weekend and have learned lots of things in the process. One of these things was a handy bit of Ruby that seemed worth sharing for other newcomers.

What I wanted to do was find out if any key from a list of keys existed in a hash. For example, given a hash animals, I'd like to know if it contains at least one key among the keys horse, frog, and cow. Checking for a single key is easy:

animals.key?('horse')

But what about when we want to check for all three of those animals? Well, we could just do one after another:

animals.key?('horse') || animals.key?('frog') || animals.key?('cow')

But that can get cumbersome very quickly. There are a few cleaner ways to do this for multiple keys, but the method I ended up using takes advantage of the fact that the Array class in Ruby includes the Enumerable module, which has a handy method called any?. This method takes a block and will return true if any invocations of the block return a "truthy" value. So, here is the solution:

['horse', 'frog', 'cow'].any? do |key|
  animals.key?(key)
end

So what is happening here? First, we're defining an array that contains all the keys we want to check for. Then we call the any? method on that array and pass it a block. Inside the block, we check if the key in the current invocation exists in animals. If an existing key is ever found, the entire call will return true. This removes some repetition and makes the code easier to read.

Note that you can also find out if the hash contains all of the keys rather than just one by using the all? method instead of any?.