[Numpy-discussion] select column based on another column value

[Georgios Exarchakis]

I think you need this

 >>> testdata[testdata[:,0]==today][:,2].mean()
4.266666666666667

 >>> testdata[testdata[:,0]==yesterday][:,2].mean()
5.633333333333334

 >>> testdata[testdata[:,0]==twodaysago][:,2].mean()
2.9333333333333336


On 10/09/2013 06:46 AM, Roelf Schreurs wrote:
>
> Hi
>
> I have the following array and want to calculate the average per day.
>
> Import numpy as np
>
> from datetime import date
>
> today =  date(today.year, today.month, 9)
>
> yesterday = date(today.year, today.month, 8)
>
> twodaysago = date(today.year, today.month, 7)
>
> testdata = np.array([[today, "r", 3.2],[today, "r", 4.3],[today, "r", 
> 5.3],[yesterday, "r", 6.3],[yesterday, "r", 9.3],[yesterday, "r", 
> 1.3],[twodaysago, "r", 3.3],[twodaysago, "r", 1.2],[twodaysago, "r", 
> 4.3]])
>
> which produces
>
> array([[datetime.date(2013, 10, 9), 'r', 3.2],
>
>        [datetime.date(2013, 10, 9), 'r', 4.3],
>
>        [datetime.date(2013, 10, 9), 'r', 5.3],
>
>        [datetime.date(2013, 10, 8), 'r', 6.3],
>
>        [datetime.date(2013, 10, 8), 'r', 9.3],
>
>        [datetime.date(2013, 10, 8), 'r', 1.3],
>
>        [datetime.date(2013, 10, 7), 'r', 3.3],
>
>        [datetime.date(2013, 10, 7), 'r', 1.2],
>
>        [datetime.date(2013, 10, 7), 'r', 4.3]], dtype=object)
>
> And I want the output as (numbers aren't correct below):
>
> 2013-10-09, 4.54
>
> 2013-10-08, 5.43
>
> 2013-10-07, 2.76
>
> But not sure how.
>
> Thanks
>
> *Roelf *
>
>
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