[SciPy-user] Table like array

Travis Oliphant oliphant at ee.byu.edu
Thu Mar 2 17:59:50 CST 2006

Michael Sorich wrote:

> On 3/1/06, *Travis Oliphant* <oliphant.travis at ieee.org 
> <mailto:oliphant.travis at ieee.org>> wrote:
>     Michael Sorich wrote:
>     > Hi,
>     >
>     > I am looking for a table like array. Something like a 'data frame'
>     > object to those familiar with the statistical languages R and Splus.
>     > This is mainly to hold and manipulate 2D spreadsheet like data,
>     which
>     > tends to be of relatively small size (compared to what many people
>     > seem to use numpy for), heterogenous, have column and row names, and
>     > often contains missing data.
>     You could subclass the ndarray to produce one of these fairly
>     easily, I
>     think.   The missing data item could be handled by a mask stored along
>     with the array (or even in the array itself).  Or you could use a
>     masked
>     array as your core object (though I'm not sure how it handles the
>     arbitrary (i.e. record-like) data-types yet).
> Thanks for the replies. You mention that missing data could be stored 
> in the array itself. Can one use nan to indicate missing data? In some 
> ways it seems more convenient to store this data in the array itself 
> rather than have a second mask array.

Yes, that's the approach I usually take for floating-point data.  There 
are some speed concerns for large arrays because I think operations with 
nans can be slower.  But, I have not tested that statement recently.


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