On 7/11/06, Stefan van der Walt <[EMAIL PROTECTED]> wrote: > On Tue, Jul 11, 2006 at 11:32:48AM +0200, Emanuele Olivetti wrote: > > Hi, > > I don't understand how to use argsort results. I have a 2D matrix and > > I want to sort values in each row and obtain the index array of that > > sorting. Argsort(1) is what I need, but the problem is how to use its > > result in order to obtain a sorted matrix. Here is the simple example: > > > > A = array([[2,3,1],[5,4,6]]) > > indexes = a.argsort(1) > > > > now indexes is: > > array([[2, 0, 1], > > [1, 0, 2]]) > > > > I'd like to apply indexes to A and obtain: > > array([[1, 2, 3], > > [4, 5, 6]]) > > > > or better, I'm interested both in a subset of indexes, i.e. indexes[:,1:], > > and > > the related values of A matrix. > > > > How can I do this? If I simpy say: A[indexes] I get an IndexError. > > Something's not quite right here. The argsort docstring states that: > > argsort(a,axis=-1) return the indices into a of the sorted array > along the given axis, so that take(a,result,axis) is the sorted array. > > But > > N.take(A,A.argsort()) breaks. Either this is a bug, or the docstring > needs to be updated. > > Cheers > Stéfan >
I think the docstring is wrong, because take doesn't do that. if you N.take(A,A.argsort(1), 1), it doesn't break but it doesn't sort A neither. Take seems to peek entire columns, but take's docstring is missing. For the argsort docstring, it may be usefull to indicate that if one do >>> ind = indices(A.shape) >>> ind[ax] = A.argsort(axis=ax) then A[ind] is the sorted array. pau ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Numpy-discussion mailing list Numpy-discussion@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/numpy-discussion
