Ruby Hash Whitelist Filter

Question

I am trying to figure out how I can filter out key and value pairs from one filter into another

For example I want to take this hash

x = { "one" => "one", "two" => "two", "three" => "three"}  y = x.some_function  y == { "one" => "one", "two" => "two"} 

Thanks for your help

EDIT: should probably mention that in this example, I want it to behave as a whitelist filter. That is, I know what I want, not what I don't want.

Answer 1

Rails' ActiveSupport library also gives you slice and except for dealing with the hash on a key level:

y = x.slice("one", "two") # => { "one" => "one", "two" => "two" } y = x.except("three")     # => { "one" => "one", "two" => "two" } x.slice!("one", "two")    # x is now { "one" => "one", "two" => "two" } 

These are quite nice, and I use them all the time.

Answer 2

Maybe this it what you want.

wanted_keys = %w[one two] x = { "one" => "one", "two" => "two", "three" => "three"} x.select { |key,_| wanted_keys.include? key } 

The Enumerable mixin which is included in e.g. Array and Hash provides a lot of useful methods like select/reject/each/etc.. I suggest that you take a look at the documentation for it with ri Enumerable.