On Fri, Sep 22, 2006 at 02:17:57AM -0500, Robert Kern wrote: > Stefan van der Walt wrote: > > Hi P., > > > > On Thu, Sep 21, 2006 at 07:40:39PM -0400, PGM wrote: > > > >> I'm running into the following problem with putmask on take. > >> > >>>>> import numpy > >>>>> x = N.arange(12.) > >>>>> m = [1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 1] > >>>>> i = N.nonzero(m)[0] > >>>>> w = N.array([-1, -2, -3, -4.]) > >>>>> x.putmask(w,m) > >>>>> x.take(i) > >>>>> N.allclose(x.take(i),w) > > > > According to the putmask docstring: > > > > a.putmask(values, mask) sets a.flat[n] = v[n] for each n where > > mask.flat[n] is true. v can be scalar. > > > > This would mean that 'w' is not of the right length. > > There are 4 true values in m and 4 values in w. What's the wrong length?
The way I read the docstring, you use putmask like this: In [4]: x = N.array([1,2,3,4]) In [5]: x.putmask([4,3,2,1],[1,0,0,1]) In [6]: x Out[6]: array([4, 2, 3, 1]) > For the sake of clarity: > > > In [1]: from numpy import * > > In [3]: m = [1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 1] > > In [4]: i = nonzero(m)[0] > > In [5]: i > Out[5]: array([ 0, 6, 9, 11]) > > In [6]: w = array([-1, -2, -3, -4.]) > > In [7]: x = arange(12.) > > In [8]: x.putmask(w, m) > > In [9]: x > Out[9]: > array([ -1., 1., 2., 3., 4., 5., -3., 7., 8., -2., 10., > -4.]) > > In [17]: x[array(m, dtype=bool)] = w > > In [18]: x > Out[18]: > array([ -1., 1., 2., 3., 4., 5., -2., 7., 8., -3., 10., > -4.]) > > > Out[9] and Out[18] should have been the same, but elements 6 and 9 are > flipped. > It's pretty clear that this is a bug in .putmask(). Based purely on what I read in the docstring, I would expect the above to do x[0] = w[0] x[6] = w[6] x[9] = w[9] x[11] = w[11] Since w is of length 4, you'll probably get indices modulo 4: w[6] == w[2] == -3 w[9] == w[1] == -2 w[11] == w[3] == -4 Which seems to explain what you are seeing. Regards Stéfan ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Numpy-discussion mailing list Numpy-discussion@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/numpy-discussion
