Numbering sequencing sets of same column values

Question

How do do numbering/sequencing for sets of the same column values? For example:

Col1 Col2
Andy  1
Chad  1
Bill  1 
Andy  2
Bill  2
Bill  3
Chad  2
Bill  4

Since Andy got 2 values, I want to number it 1 and 2 in Column 2. For Bill, I want to number it 1, 2, 3 and 4, and so on.

Answer 1

You can accomplish this with countif and a sliding range :

   A        B
1  val1     =COUNTIF($A$1:A1, A1)
2  valx     =COUNTIF($A$1:A2, A2)

And so on.

The formula in column B can be automatically filled in or moved down into the column. COUNTIF counts up the matching values in the previous set in this fashion; it anchors to the top of the range and only scans down to the value we are numbering.