[Numpy-discussion] array of random numbers fails to construct
Allan Haldane
allanhaldane at gmail.com
Sun Dec 6 18:55:50 EST 2015
I've also often wanted to generate large datasets of random uint8 and
uint16. As a workaround, this is something I have used:
np.ndarray(100, 'u1', np.random.bytes(100))
It has also crossed my mind that np.random.randint and np.random.rand
could use an extra 'dtype' keyword. It didn't look easy to implement though.
Allan
On 12/06/2015 04:55 PM, DAVID SAROFF (RIT Student) wrote:
> Matthew,
>
> That looks right. I'm concluding that the .astype(np.uint8) is applied
> after the array is constructed, instead of during the process. This
> random array is a test case. In the production analysis of radio
> telescope data this is how the data comes in, and there is no problem
> with 10GBy files.
> linearInputData = np.fromfile(dataFile, dtype = np.uint8, count = -1)
> spectrumArray = linearInputData.reshape(nSpectra,sizeSpectrum)
>
>
> On Sun, Dec 6, 2015 at 4:07 PM, Matthew Brett <matthew.brett at gmail.com
> <mailto:matthew.brett at gmail.com>> wrote:
>
> Hi,
>
> On Sun, Dec 6, 2015 at 12:39 PM, DAVID SAROFF (RIT Student)
> <dps7802 at rit.edu <mailto:dps7802 at rit.edu>> wrote:
> > This works. A big array of eight bit random numbers is constructed:
> >
> > import numpy as np
> >
> > spectrumArray = np.random.randint(0,255, (2**20,2**12)).astype(np.uint8)
> >
> >
> >
> > This fails. It eats up all 64GBy of RAM:
> >
> > spectrumArray = np.random.randint(0,255, (2**21,2**12)).astype(np.uint8)
> >
> >
> > The difference is a factor of two, 2**21 rather than 2**20, for the extent
> > of the first axis.
>
> I think what's happening is that this:
>
> np.random.randint(0,255, (2**21,2**12))
>
> creates 2**33 random integers, which (on 64-bit) will be of dtype
> int64 = 8 bytes, giving total size 2 ** (21 + 12 + 6) = 2 ** 39 bytes
> = 512 GiB.
>
> Cheers,
>
> Matthew
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> --
> David P. Saroff
> Rochester Institute of Technology
> 54 Lomb Memorial Dr, Rochester, NY 14623
> david.saroff at mail.rit.edu <mailto:david.saroff at mail.rit.edu> | (434)
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