[Numpy-discussion] Medians that ignore values
paul taney
paultaney@yahoo....
Thu Sep 18 11:36:27 CDT 2008
Hi,
> >>> median(m.T)
> array([ 1.00000000e+20, 2.12298948e-01, 3.57822574e-01,
I believe 1.00000000e+20 is a reserved value and signifys the
missing value or NaN in your case. That"s the way it was in
a Fortran77 package I worked with ten years ago...
--- On Thu, 9/18/08, Peter Saffrey <pzs@dcs.gla.ac.uk> wrote:
> From: Peter Saffrey <pzs@dcs.gla.ac.uk>
> Subject: Re: [Numpy-discussion] Medians that ignore values
> To: numpy-discussion@scipy.org
> Date: Thursday, September 18, 2008, 10:59 AM
> <jh <at> physics.ucf.edu> writes:
>
> > Currently the only way you can handle NaNs is by
> using masked arrays.
> > Create a mask by doing isfinite(a), then call the
> masked array
> > median(). There's an example here:
> >
> > http://sd-2116.dedibox.fr/pydocweb/doc/numpy.ma/
> >
>
> I had looked at masked arrays, but couldn't quite get
> them to work.
> Generating them is fine (I've randomly introduced a few
> nan values into
> this array):
>
> >>> from numeric import *
> >>> from pylab import rand
> >>> a = rand(10,3)
> >>> a[a > 0.8] = nan
> >>> m = ma.masked_array(a, isnan(a))
> >>> m
> array(data =
> [[ 5.97400164e-01 1.00000000e+20 1.00000000e+20]
> [ 3.34623242e-01 6.53582662e-02 2.12298948e-01]
> [ 2.11879853e-01 1.00000000e+20 3.57822574e-01]
> [ 6.06911592e-01 1.96229341e-01 5.49953059e-02]
> [ 1.00000000e+20 2.75493584e-01 4.70929957e-01]
> [ 2.92845118e-01 2.11261529e-02 3.49211381e-02]
> [ 7.11963636e-01 2.17277855e-01 5.45487384e-02]
> [ 5.20995579e-01 7.57676845e-01 1.00000000e+20]
> [ 1.84189196e-01 7.58291436e-02 6.26567116e-01]
> [ 2.42083978e-01 1.00000000e+20 2.30202562e-02]],
> mask =
> [[False True True]
> [False False False]
> [False True False]
> [False False False]
> [ True False False]
> [False False False]
> [False False False]
> [False False True]
> [False False False]
> [False True False]],
> fill_value=1e+20)
>
>
> Remember I want medians of each triple, so I need to median
> the
> transposed matrix:
>
> >>> median(m.T)
> array([ 1.00000000e+20, 2.12298948e-01,
> 3.57822574e-01,
> 1.96229341e-01, 4.70929957e-01,
> 3.49211381e-02,
> 2.17277855e-01, 7.57676845e-01,
> 1.84189196e-01,
> 2.42083978e-01])
>
> The first value is NaN, indicating that the median routine
> has failed to
> ignore the masked values. What have I missed?
>
> Thanks,
>
> Peter
> _______________________________________________
> Numpy-discussion mailing list
> Numpy-discussion@scipy.org
> http://projects.scipy.org/mailman/listinfo/numpy-discussion
More information about the Numpy-discussion
mailing list