Heading in Table Form Question

Question

I have:

modadd = Table[Mod[i + j, 3], {i, 0, 2}, {j, 0, 2}];
TableForm[modadd,
 TableHeadings -> {{0, 1, 2}, {0, 1, 2}}]

Which produces:

How can I put a plus sign in the upper left hand corner, making the first row of headings +, 0, 1, and 2.

Answer 1

I'm afraid that you are going to have to build your own Grid for that. I don't think that the top left position is accessible through TableHeadings:

Grid[
 Insert[Transpose@Join[{Range[0, 2]}, modadd], Flatten[{"+", Range[0, 2]}], 1],
 Dividers -> {{False, True, False}, {False, True, False}}
]

---

Here's a helper function to generate these grids automatically:

Clear[modaddition]
modaddition[modulo_Integer] :=
 Grid[
   SparseArray[{
     {1, 1} -> "+",
     {1, i_} -> i - 2,
     {j_, 1} -> j - 2,
     {i_, j_} /; i != 1 && j != 1 -> Mod[i + j - 4, modulo]
    }, 
    {modulo + 1, modulo + 1}
   ],
   Dividers -> {{False, True}, {False, True}}
 ]


modaddition[5]