related lists mean value

[MRAB]

dimitri pater - serpia wrote:
> Hi,
> 
> I have two related lists:
> x = [1 ,2, 8, 5, 0, 7]
> y = ['a', 'a', 'b', 'c', 'c', 'c' ]
> 
> what I need is a list representing the mean value of 'a', 'b' and 'c'
> while maintaining the number of items (len):
> w = [1.5, 1.5, 8, 4, 4, 4]
> 
> I have looked at iter(tools) and next(), but that did not help me. I'm
> a bit stuck here, so your help is appreciated!
> 
Try doing it in 2 passes.

First pass: count the number of times each string occurs in 'y' and the
total for each (zip/izip and defaultdict are useful for these).

Second pass: create the result list containing the mean values.