{ val1 => [-1], # val1 occurs more than once in col 1 val2 => [2, 1], # val2 occurs once in col 1 and once in col 2 val3 => [-3, 1], #val3 occurs more than once in col 3 #but only one time in col1 val4 => [-2], val5 => [-3], val6 => [1], val7 => [-2], #val7 is mentioned at least twice in col2 }