A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Copy the code for the ConcatenateIf function from http://eileenslounge.com/viewtopic.php?p=91187#p91187 into a module in the Visual Basic Editor.
You can then use the following formula in C1:
=ConcatenateIf($A$1:$A$13,$A1,$B$1:$B$13)
and fill down. Adjust the ranges as needed.
Alternatively:
In C1, enter =B1.
In C2, enter =IF(B2=B1,C1&B2,B2)
Fill down from C2 to the end of the data. The last entry for each unique value in column A will contain the merged value.