2013/11/26 Peter Prettenhofer <peter.prettenho...@gmail.com>: > Hi all, > > I'm currently modifying our tree code so that it runs on both fortran and c > continuous arrays. After some benchmarking I got aware of the following > numpy behavior that was contrary to what I was expecting:: > > >>> X = # some feature matrix > >>> X = np.asfortranarray(X) > >>> X.flags.f_contiguous > True > >>> # so far so good > >>> X_train = X[:1000] > >>> X_train.flags.f_contiguous > False > >>> X_train.flags.c_contiguous > False > >>> # damn - seems like a view is neither c nor fortran continuous
Only if you slice the rows of a fortran aligned 2D array, this is expected. If you slices the rows of a C-contiguous 2D array or the columns of a F-contiguous 2D array it stays contiguous. >>> import numpy as np >>> a_c = np.arange(12).reshape(3, 4) >>> a_f = np.asfortranarray(a_c) >>> a_c.flags C_CONTIGUOUS : True F_CONTIGUOUS : False OWNDATA : False WRITEABLE : True ALIGNED : True UPDATEIFCOPY : False >>> a_f.flags C_CONTIGUOUS : False F_CONTIGUOUS : True OWNDATA : True WRITEABLE : True ALIGNED : True UPDATEIFCOPY : False >>> a_c[1:].flags C_CONTIGUOUS : True F_CONTIGUOUS : False OWNDATA : False WRITEABLE : True ALIGNED : True UPDATEIFCOPY : False >>> a_f[:, 1:].flags C_CONTIGUOUS : False F_CONTIGUOUS : True OWNDATA : False WRITEABLE : True ALIGNED : True UPDATEIFCOPY : False -- Olivier http://twitter.com/ogrisel - http://github.com/ogrisel ------------------------------------------------------------------------------ Shape the Mobile Experience: Free Subscription Software experts and developers: Be at the forefront of tech innovation. Intel(R) Software Adrenaline delivers strategic insight and game-changing conversations that shape the rapidly evolving mobile landscape. Sign up now. http://pubads.g.doubleclick.net/gampad/clk?id=63431311&iu=/4140/ostg.clktrk _______________________________________________ Scikit-learn-general mailing list Scikit-learn-general@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/scikit-learn-general
