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@gmail.com
<mailto:matthew.brett@gmail.com>> wrote:
Hi,
On Sun, Dec 6, 2015 at 12:39 PM, DAVID SAROFF (RIT Student)
<dps7802@rit.edu <mailto:dps7802@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
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