Remove trailing nil values from array in ruby

For this you can forget about the outer array and solve it for just the inner arrays, then use map to apply the solution to all of them.

drop_while will return a new array without all leading items that met some condition (e.g. nil?). You wanted trailing however so combine with reverse.

[nil,nil,5,nil,6,nil].reverse.drop_while(&:nil?).reverse
[nil, nil, 5, nil, 6]

Then use map for all the arrays.

arr = [["a", nil, nil, nil], ["b", nil, "c", nil], [nil, nil, nil, nil]]
arr.map{|a| a.reverse.drop_while(&:nil?).reverse}
[["a"], ["b", nil, "c"], []]

If you do want any remaining nil to actually be a string, you could combine it with another map performing any such conversion you like.

You are on the right way, but just modify your code a bit:

array.each { |e| e.pop until !e.last.nil? || e.empty? }
#=> [["a"], ["b", nil, "c"], []]

It's faster than using reverse-reverse and drop_while.

One more option is to use rindex:

arr.map do |e| 
  index =  e.rindex { |i| !i.nil? } # the last index of not `nil` element
  index ? e.first(index + 1) : e 
end
#=> [["a"], ["b", nil, "c"], []]