func hashJoin(table1, index1, table2, index2) {
    var a = []
    var h = Hash()

    # hash phase
    table1.each { |s|
        h{s[index1]} := [] << s
    }

    # join phase
    table2.each { |r|
        a += h{r[index2]}.map{[_,r]}
    }

    return a
}

var t1  = [[27, "Jonah"],
           [18, "Alan"],
           [28, "Glory"],
           [18, "Popeye"],
           [28, "Alan"]]

var t2  = [["Jonah", "Whales"],
           ["Jonah", "Spiders"],
           ["Alan", "Ghosts"],
           ["Alan", "Zombies"],
           ["Glory", "Buffy"]]

hashJoin(t1, 1, t2, 0).each { .say }