Can someone explain the function of colon here?

Question

Can someone explain what : does in this case?

def group_by_marks(marks, n)
    marks.group_by {|key, value| value <n ? "Failed" : "Passed"}
end

Answer 1

That is a ternary condition. The colon says that if value is greater than or equal to n, use "Passed".

value < n ? "Failed" : "Passed"

Equivalent to

if value < n then "Failed" else "Passed" end

Answer 2

It's ternary operator. If value < n is true, then the return value of this block is "Failed"; if value < n is false, return "Passed".

You can simply regard this colon as "either this or that".