ruby - what's a clean way of finding which common elements exist in a set of n arrays? -

i'm going through table in database has lot of optional columns. i'm wanting find columns have data in every record in database.

a simplified example of i'm trying follows:

[1,2,3,4,5] & [1,2,3,4] & [1,2,3] & [1,2] #=> [1,2] 

however, i'm trying run type of operation thousands of records. what's clean way accomplish this? have feeling ruby might have bespoke methods sort of thing.

here's before decided write question:

sets_of_columns_with_data = tablename.all.map(&:attributes).map |attrs|      attrs.select {|k,v| v} end.map(&:keys) 

so @ point, if following above code, columns_with_data equivalent of this:

sets_of_columns_with_data = [   [1,2,3,4,5],   [1,2,3,4],   [1,2,3]   [1,2]  ] 

a messy way guess this:

always_used = sets_of_columns_with_data.first sets_of_columns_with_data.each |columns_with_data|   always_used = always_used & columns_with_data end 

what's clean, ruby-way this?

thanks

note:

i'm keeping business logic sake of clarity, not best solution when have sql available you.

i'm not sure if solves actual problem, apply binary operation, can use reduce:

sets_of_columns_with_data = [   [1, 2, 3, 4, 5],   [1, 2, 3, 4],   [1, 2, 3],   [1, 2] ]  sets_of_columns_with_data.reduce(:&) #=> [1, 2]