As the subject says, numpy.concatenate doesn't seem to obey -- or even check -- the axis flag when concatenating 1D arrays:
----------------------- <session log> ----------------- In [30]: A = numpy.array([1, 2, 3, 4]) In [31]: D = numpy.array([6, 7, 8, 9]) In [32]: numpy.concatenate((A, D)) Out[32]: array([1, 2, 3, 4, 6, 7, 8, 9]) In [33]: numpy.concatenate((A, D), axis=0) Out[33]: array([1, 2, 3, 4, 6, 7, 8, 9]) In [34]: numpy.concatenate((A, D), axis=1) Out[34]: array([1, 2, 3, 4, 6, 7, 8, 9]) In [35]: numpy.concatenate((A, D), axis=2) Out[35]: array([1, 2, 3, 4, 6, 7, 8, 9]) ----------------------- </session log> ----------------- However, if you create the same arrays as 2D (1xn) arrays, then numpy checks, and does the right thing: ---------------------- <session log> ------------------- In [36]: A = numpy.array([[1, 2, 3, 4]]) In [37]: D = numpy.array([[6, 7, 8, 9]]) In [38]: A.shape Out[38]: (1, 4) In [39]: numpy.concatenate((A, D)) Out[39]: array([[1, 2, 3, 4], [6, 7, 8, 9]]) In [40]: numpy.concatenate((A, D), axis=0) Out[40]: array([[1, 2, 3, 4], [6, 7, 8, 9]]) In [41]: numpy.concatenate((A, D), axis=1) Out[41]: array([[1, 2, 3, 4, 6, 7, 8, 9]]) In [42]: numpy.concatenate((A, D), axis=2) --------------------------------------------------------------------------- <type 'exceptions.ValueError'> Traceback (most recent call last) /fs/home/sdb/<ipython console> in <module>() <type 'exceptions.ValueError'>: bad axis1 argument to swapaxes ----------------------- </session log> ----------------- Question: Is is a bug or a feature? I'd at least think that numpy would check the axis arg in the 1D case, and issue an error if the user tried to do something impossible (e.g. axis=2). Whether numpy would promote a 1D to a 2D array is a different question, and I am agnostic about that one. Cheers, Stuart Brorson Interactive Supercomputing, inc. 135 Beaver Street | Waltham | MA | 02452 | USA http://www.interactivesupercomputing.com/ _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion