On 8/29/06, Mathew Yeates wrote:

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.

Make a cumsum of the array. Find the index of the last 'a', last 'b', etc and make the reduced array from that. Then take the diff of the columns. I know that's vague, but so is my understanding of python/numpy. Or even more vague: make a function that does what you want.

Mathew Yeates schrieb:

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.

Hi, I don't have time for this ;-) , but I learnt something useful along the way... import numpy as n m = n.ones([2,6]) a = ['b', 'c', 'c', 'd', 'd', 'd'] startindices = set([a.index(x) for x in a]) out = n.empty([m.shape[0], 0]) for i in startindices: temp = n.mat(m[:, i : i + a.count(a[i])]).sum(axis = 1) out = n.hstack([out, temp]) print out Not sure if axis = 1 is needed, but until the defaults have settled a bit it can't hurt. You need python 2.4 for the built-in <set>, and <out> will be a numpy matrix, use <asarray> if you don't like that. But here it's really nice to work with matrices, because otherwise .sum() will give you a 1-d array sometimes, and that will suddenly look like a row to <hstack> (instead of a nice column vector) and wouldn't work -- that's why matrices are so great and everybody should be using them ;-) hth, sven

On Tue, Aug 29, 2006 at 03:46:45PM -0700, Mathew Yeates wrote:

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.

I attach one possible solution (allowing for the same column name occurring in different places, i.e. ['a','b','b','a']). I'd be glad for any suggestions on how to clean up the code. Regards Stéfan