[Numpy-discussion] Re: What am I missing about concatenate? (original) (raw)

Christopher Barker Chris.Barker at noaa.gov
Thu Jun 1 12:14:01 EDT 2006

Thanks all,

Robert Kern wrote:

Look at vstack() (and also its friends hstack(), dstack() and columnstack() for completeness).

I like this, but need to keep Numeric/numarray compatibility for the moment -- I think, I've just sent out a query to my users.

Tim Hochberg wrote:

If you are using real arrays, use newaxis:

>>> a array([0, 1, 2]) >>> b array([3, 4, 5]) >>> concatenate([a[newaxis], b[newaxis]], 0) array([[0, 1, 2], [3, 4, 5]])

I like this, but again, not in Numeric -- I really need to dump that as soon as I can!

hate newaxis, wrap the arrays in [] to give them an extra dimension. This tends to look nicer, but I suspect has poorer performance than above (haven't timed it though):

>>> concatenate([[a], [b]], 0) array([[0, 1, 2], [3, 4, 5]])

Lovely. much cleaner.

By they way, wouldn't wrapping in a tuple, be slightly better, performance-wise (I know, probably negligible, but I always feel that I should use a tuple when I don't need mutability)

-thanks,

-chris

-- Christopher Barker, Ph.D. Oceanographer

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