wolfram-mathematica

Comparing lists in Mathematica

I want to compare two lists in Mathematica, see what elements in the first list are not in, the second list, and then print out the non-equal elements. I generated two lists and I want to use a for loop to go through the two lists and compare each element.

Solution 
  • list1 = {3, 56, 9, 8, 7, 33, 5};
list2 = {33, 4, 56, 7, 9, 23};

    The usual idiom would be Complement. Note, it sorts the output.

    notinlist2 = Complement[list1, list2]
notinlist1 = Complement[list2, list1]

    {3, 5, 8}
{4, 23}

    Using a For loop preserves the order from list1

    notinlist2 = {};

For[i = 1, i <= Length[list1], i++,
 If[FreeQ[list2, list1[[i]]],
  AppendTo[notinlist2, list1[[i]]]]]

notinlist2

    {3, 8, 5}

    The same can be achieved with DeleteDuplicates

    Drop[DeleteDuplicates[Join[list2, list1]], Length[list2]]

    {3, 8, 5}