How does one wrap numpy array types?

Question

I'd like to make a class extending the numpy array base type,

class LemmaMatrix(numpy.ndarray):
    @classmethod
    def init_from_corpus(cls, ...): cls(numpy.empty(...))

But apparently, it will not allow multi-dimensional array types. Is there a way around this? Thanks in advance!

ndarray(empty([3, 3]))
TypeError: only length-1 arrays can be converted to Python scalars

unutbu · Accepted Answer · 2010-05-17 22:00:32Z

5

import numpy as np
class LemmaMatrix(np.ndarray):
    def __new__(subtype,data,dtype=None):
        subarr=np.empty(data,dtype=dtype)
        return subarr

lm=LemmaMatrix([3,3])
print(lm)
# [[  3.15913337e-260   4.94951870e+173   4.88364603e-309]
#  [  1.63321355e-301   4.80218258e-309   2.05227026e-287]
#  [  2.10277051e-309   2.07088188e+289   7.29366696e-304]]

You may also want read this guide for more information on how to subclass ndarray.

answered May 17, 2010 at 22:00

unutbu

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3 Comments

gatoatigrado Over a year ago

That looks great; the numpy.empty.view(LemmaMatrix) also seems good. Thanks! :)

gatoatigrado Over a year ago

One minor thing -- why not $size instead of $data? It is the dimensions, not the values, clearly?

unutbu Over a year ago

@gatoatigrado: By all means, you could use something like np.array(data).size. I was guessing -- perhaps incorrectly -- what you wanted.

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