Ruby Hash Filter

Question

Hello

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

Answer 1

You can just use the built in Hash function reject.

x = { "one" => "one", "two" => "two", "three" => "three"}
y = x.reject {|key,value| key == "three" }
y == { "one" => "one", "two" => "two"}

You can put whatever logic you want into the reject, and if the block returns true it will skip that key,value in the new hash.

Answer 2

y = x.reject {|k,v| k == "three"}

Answer 3

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.

Answer 4

Using a combination of everyones answers I have come up with this solution

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

Thanks for your help guys!

Answer 5

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

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