Hi all, How can I delete a column/row from a matrix. In Matlab:
a=rand(4,4)
a = 0.9501 0.8913 0.8214 0.9218 0.2311 0.7621 0.4447 0.7382 0.6068 0.4565 0.6154 0.1763 0.4860 0.0185 0.7919 0.4057 use
a(:,2)=[]
a = 0.9501 0.8214 0.9218 0.2311 0.4447 0.7382 0.6068 0.6154 0.1763 0.4860 0.7919 0.4057
a(2,:)=[]
a = 0.9501 0.8214 0.9218 0.6068 0.6154 0.1763 0.4860 0.7919 0.4057
Is there something similar in scipy, numpy or numarray ? Any suggestion ? Nils
How can I delete a column/row from a matrix.
As an in-place operation, not at all. To get a copy of an array with some columns/rows removed, use Numeric.take. Konrad. -- ------------------------------------------------------------------------------- Konrad Hinsen | E-Mail: hinsen@cnrs-orleans.fr Centre de Biophysique Moleculaire (CNRS) | Tel.: +33-2.38.25.56.24 Rue Charles Sadron | Fax: +33-2.38.63.15.17 45071 Orleans Cedex 2 | Deutsch/Esperanto/English/ France | Nederlands/Francais -------------------------------------------------------------------------------
Konrad Hinsen schrieb:
How can I delete a column/row from a matrix.
As an in-place operation, not at all. To get a copy of an array with some columns/rows removed, use Numeric.take.
The in-place operation of matlab is a nice feature. Is it thinkable to have this in scipy or numarray at a later date ? Nils
Konrad. -- ------------------------------------------------------------------------------- Konrad Hinsen | E-Mail: hinsen@cnrs-orleans.fr Centre de Biophysique Moleculaire (CNRS) | Tel.: +33-2.38.25.56.24 Rue Charles Sadron | Fax: +33-2.38.63.15.17 45071 Orleans Cedex 2 | Deutsch/Esperanto/English/ France | Nederlands/Francais -------------------------------------------------------------------------------
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Konrad Hinsen schrieb:
How can I delete a column/row from a matrix.
As an in-place operation, not at all. To get a copy of an array
with some
columns/rows removed, use Numeric.take.
The in-place operation of matlab is a nice feature. Is it thinkable to have this in scipy or numarray at a later date ?
Nils
Speaking for numarray, no, not really. But I wonder what is really done for matlab. Either they have a more complex representation of arrays, or all they really are doing is making a new copy of the array and giving you the impression it is being done in place. After all you are changing the size and structure of the array. Perry
On Mon, 2003-07-28 at 07:34, Perry Greenfield wrote:
Speaking for numarray, no, not really. But I wonder what is really done for matlab. Either they have a more complex representation of arrays, or all they really are doing is making a new copy of the array and giving you the impression it is being done in place.
Right, this is how Matlab does it behind the scenes. Ralf
On Monday 28 July 2003 16:26, Nils Wagner wrote:
Konrad Hinsen schrieb:
How can I delete a column/row from a matrix.
As an in-place operation, not at all. To get a copy of an array with some columns/rows removed, use Numeric.take.
The in-place operation of matlab is a nice feature. Is it thinkable to have this in scipy or numarray at a later date ?
I'd say that the obvious way to implement it is as del a[2:3,:] That can certainly be done, but someone has to do it. Personally, I am not convinced that it is very useful. The consequences of an in-place change can be disastrous when many references point to that array. But then, we have other in-place operations which sometimes are handy, so my usefulness estimation may be wrong. Konrad. -- ------------------------------------------------------------------------------- Konrad Hinsen | E-Mail: hinsen@cnrs-orleans.fr Centre de Biophysique Moleculaire (CNRS) | Tel.: +33-2.38.25.56.24 Rue Charles Sadron | Fax: +33-2.38.63.15.17 45071 Orleans Cedex 2 | Deutsch/Esperanto/English/ France | Nederlands/Francais -------------------------------------------------------------------------------
Konrad Hinsen schrieb:
On Monday 28 July 2003 16:26, Nils Wagner wrote:
Konrad Hinsen schrieb:
How can I delete a column/row from a matrix.
As an in-place operation, not at all. To get a copy of an array with some columns/rows removed, use Numeric.take.
The in-place operation of matlab is a nice feature. Is it thinkable to have this in scipy or numarray at a later date ?
I'd say that the obvious way to implement it is as
del a[2:3,:]
That can certainly be done, but someone has to do it.
Personally, I am not convinced that it is very useful. The consequences of an in-place change can be disastrous when many references point to that array. But then, we have other in-place operations which sometimes are handy, so my usefulness estimation may be wrong.
Konrad.
In my opinion, this operation is quite useful. For example a finite element model where we have to impose several homogeneous boundary conditions. This can be done by deleting columns and associated rows. Nils In any case I am interested in a reliable workaround for this feature. A small example would be appreciated. Thanks in advance.
-- ------------------------------------------------------------------------------- Konrad Hinsen | E-Mail: hinsen@cnrs-orleans.fr Centre de Biophysique Moleculaire (CNRS) | Tel.: +33-2.38.25.56.24 Rue Charles Sadron | Fax: +33-2.38.63.15.17 45071 Orleans Cedex 2 | Deutsch/Esperanto/English/ France | Nederlands/Francais -------------------------------------------------------------------------------
------------------------------------------------------- This SF.Net email sponsored by: Free pre-built ASP.NET sites including Data Reports, E-commerce, Portals, and Forums are available now. Download today and enter to win an XBOX or Visual Studio .NET. http://aspnet.click-url.com/go/psa00100003ave/direct;at.aspnet_072303_01/01 _______________________________________________ Numpy-discussion mailing list Numpy-discussion@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/numpy-discussion
participants (4)
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Konrad Hinsen -
Nils Wagner -
Perry Greenfield -
Ralf Juengling