[Numpy-discussion] insanely slow writing to memory mapped array

Charles R Harris charlesr.harris at gmail.com
Wed Nov 29 21:18:15 CST 2006


On 11/29/06, Mathew Yeates <myeates at jpl.nasa.gov> wrote:
>
> whoa. I just found out that A=A.transpose() does nothing but change A's
> flags from C_CONTIGUOUS to F_CONTIGUOUS!!
>
> Okay, so heres the question ...... I am reading data into the columns of
> a matrix. In order to speed this up, I want to read values into the rows
> of a matrix and when I am all done, do a transpose. Whats the best way?


If you want a contiguous copy

In [13]: a
Out[13]:
array([[0, 1, 2, 3, 4],
       [5, 6, 7, 8, 9]])

In [14]: b=a.transpose().copy()

In [15]: a.flags
Out[15]:
  C_CONTIGUOUS : True
  F_CONTIGUOUS : False
  OWNDATA : False
  WRITEABLE : True
  ALIGNED : True
  UPDATEIFCOPY : False

In [16]: b.flags
Out[16]:
  C_CONTIGUOUS : True
  F_CONTIGUOUS : False
  OWNDATA : True
  WRITEABLE : True
  ALIGNED : True
  UPDATEIFCOPY : False

The result isn't memory mapped, however. What exactly are you trying to do?

Chuck
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