[Numpy-discussion] stumped numpy user seeks help

My head is about to explode. I have an M by N array of floats. Associated with the columns are character labels ['a','b','b','c','d','e','e','e'] note: already sorted so duplicates are contiguous I want to replace the 2 'b' columns with the sum of the 2 columns. Similarly, replace the 3 'e' columns with the sum of the 3 'e' columns. The resulting array still has M rows but less than N columns. Anyone? Could be any harder than Sudoku. Mathew