Question

I have two lists:

a = [1,2,3]
b = ["a","b","c"]

my list l is:

l = [a,b].flatten 

so l = [1,2,3,"a","b","c"]

I’m looking for an elegant way of splitting the list by the type of the items in it, in order to have a and b restored as they were.

I could go with each item in the list and test, but that doesn’t seem efficient runtime-wise nor code-wise.

Answer 1

You could use group_by and then pull your arrays out of the resulting Hash:

>> by_class = l.group_by(&:class)
=> {Integer=>[1, 2, 3], String=>["a", "b", "c"]}
>> a = by_class[Fixnum]
=> [1, 2, 3]
>> b = by_class[String]
=> ["a", "b", "c"]

If you know that you only have Fixnums and Strings then you could use partition:

>> a, b = *l.partition { |o| o.is_a? Fixnum }
=> [[1, 2, 3], ["a", "b", "c"]]
>> a
=> [1, 2, 3]
>> b
=> ["a", "b", "c"]