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Date: Fri, 21 Sep 2012 00:58:03 +0100
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Subject: Re: looping in array vs looping in a dic
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On 2012-09-21 00:35, giuseppe.amatulli@gmail.com wrote:
> Hi Ian and MRAB
> thanks to you input i have improve the speed  of my code. Definitely reading in dic() is faster. I have one more question.
> In the dic() I calculate the sum of the values, but i want count also the number of observation, in order to calculate the average in the end.
> Should i create a new dic() or is possible to do in the same dic().
> Here in the final code.
> Thanks Giuseppe
>
Keep it simple. Use 2 dicts.

>
>
> rows = dsCategory.RasterYSize
> cols = dsCategory.RasterXSize
>
> print("Generating output file %s" %(dst_file))
>
> start = time()
>
> unique=dict()
>
> for irows in xrange(rows):
>      valuesRaster=dsRaster.GetRasterBand(1).ReadAsArray(0,irows,cols,1)
>      valuesCategory=dsCategory.GetRasterBand(1).ReadAsArray(0,irows,cols,1)
>      for icols in xrange(cols):
>          if ( valuesRaster[0,icols] != no_data_Raster ) and ( valuesCategory[0,icols] != no_data_Category ) :
>              row = valuesCategory[0, icols],valuesRaster[0, icols]
>              if row[0] in unique :
>                  unique[row[0]] += row[1]
>              else:
>                  unique[row[0]] = 0+row[1] # this 0 was add if not the first observation was considered = 0
>
You could use defaultdict instead:

from collections import defaultdict

unique = defaultdict(int)
...
              category, raster = valuesCategory[0, icols], 
valuesRaster[0, icols]
              unique[category] += raster