Fastest Way to generate 1,000,000+ random numbers in python


I am currently writing an app in python that needs to generate large amount of random numbers, FAST. Currently I have a scheme going that uses numpy to generate all of the numbers in a giant batch (about ~500,000 at a time). While this seems to be faster than python’s implementation. I still need it to go faster. Any ideas? I’m open to writing it in C and embedding it in the program or doing w/e it takes.

Constraints on the random numbers:

  • A Set of 7 numbers that can all have different bounds:
    • eg: [0-X1, 0-X2, 0-X3, 0-X4, 0-X5, 0-X6, 0-X7]
    • Currently I am generating a list of 7 numbers with random values from [0-1) then multiplying by [X1..X7]
  • A Set of 13 numbers that all add up to 1
    • Currently just generating 13 numbers then dividing by their sum

Any ideas? Would pre calculating these numbers and storing them in a file make this faster?


Asked By: Sandro



EDIT Created functions that return the full set of numbers, not just one row at a time.
EDIT 2 Make the functions more pythonic (and faster), add solution for second question

For the first set of numbers, you might consider numpy.random.randint or numpy.random.uniform, which take low and high parameters. Generating an array of 7 x 1,000,000 numbers in a specified range seems to take < 0.7 second on my 2 GHz machine:

def LimitedRandInts(XLim, N):
    rowlen = (1,N)
    return [np.random.randint(low=0,high=lim,size=rowlen) for lim in XLim]

def LimitedRandDoubles(XLim, N):
    rowlen = (1,N)
    return [np.random.uniform(low=0,high=lim,size=rowlen) for lim in XLim]

>>> import numpy as np
>>> N = 1000000 #number of randoms in each range
>>> xLim = [x*500 for x in range(1,8)] #convenient limit generation
>>> fLim = [x/7.0 for x in range(1,8)]
>>> aa = LimitedRandInts(xLim, N)
>>> ff = LimitedRandDoubles(fLim, N)

This returns integers in [0,xLim-1] or floats in [0,fLim). The integer version took ~0.3 seconds, the double ~0.66, on my 2 GHz single-core machine.

For the second set, I used @Joe Kingston’s suggestion.

def SumToOneRands(NumToSum, N):
    aa = np.random.uniform(low=0,high=1.0,size=(NumToSum,N)) #13 rows by 1000000 columns, for instance
    s = np.reciprocal(aa.sum(0))
    aa *= s
    return aa.T #get back to column major order, so aa[k] is the kth set of 13 numbers

>>> ll = SumToOneRands(13, N)

This takes ~1.6 seconds.

In all cases, result[k] gives you the kth set of data.

Answered By: mtrw

Making your code run in parallel certainly couldn’t hurt. Try adapting it for SMP with Parallel Python

Answered By: Jon W

You can speed things up a bit from what mtrw posted above just by doing what you initially described (generating a bunch of random numbers and multiplying and dividing accordingly)…

Also, you probably already know this, but be sure to do the operations in-place (*=, /=, +=, etc) when working with large-ish numpy arrays. It makes a huge difference in memory usage with large arrays, and will give a considerable speed increase, too.

In [53]: def rand_row_doubles(row_limits, num):
   ....:     ncols = len(row_limits)
   ....:     x = np.random.random((num, ncols))
   ....:     x *= row_limits                  
   ....:     return x                          
In [59]: %timeit rand_row_doubles(np.arange(7) + 1, 1000000)
10 loops, best of 3: 187 ms per loop

As compared to:

In [66]: %timeit ManyRandDoubles(np.arange(7) + 1, 1000000)
1 loops, best of 3: 222 ms per loop

It’s not a huge difference, but if you’re really worried about speed, it’s something.

Just to show that it’s correct:

In [68]: x.max(0)
array([ 0.99999991,  1.99999971,  2.99999737,  3.99999569,  4.99999836,
        5.99999114,  6.99999738])

In [69]: x.min(0)
array([  4.02099599e-07,   4.41729377e-07,   4.33480302e-08,
         7.43497138e-06,   1.28446819e-05,   4.27614385e-07,

Likewise, for your “rows sum to one” part…

In [70]: def rand_rows_sum_to_one(nrows, ncols):
   ....:     x = np.random.random((ncols, nrows))
   ....:     y = x.sum(axis=0)
   ....:     x /= y
   ....:     return x.T

In [71]: %timeit rand_rows_sum_to_one(1000000, 13)
1 loops, best of 3: 455 ms per loop

In [72]: x = rand_rows_sum_to_one(1000000, 13)

In [73]: x.sum(axis=1)
Out[73]: array([ 1.,  1.,  1., ...,  1.,  1.,  1.])

Honestly, even if you re-implement things in C, I’m not sure you’ll be able to beat numpy by much on this one… I could be very wrong, though!

Answered By: Joe Kington

Try r = 1664525*r + 1013904223
from “an even quicker generator”
in “Numerical Recipes in C” 2nd edition, Press et al., isbn 0521431085, p. 284.
np.random is certainly “more random”; see
Linear congruential generator .

In python, use np.uint32 like this:

python -mtimeit -s '
import numpy as np
r = 1
r = np.array([r], np.uint32)[0]  # 316 py -> 16 us np 
    # python longs can be arbitrarily long, so slow
' '
r = r*1664525 + 1013904223  # NR2 p. 284

To generate big blocks at a time:

# initialize --
np.random.seed( ... )
R = np.random.randint( 0, np.iinfo( np.uint32 ).max, size,  dtype=np.uint32 )
R *= 1664525
R += 1013904223
Answered By: denis

As others have already pointed out, numpy is a very good start, fast and easy to use.

If you need random numbers on a massive scale, consider eas-ecb or rc4. Both can be parallelised, you should reach performance in several GB/s.

achievable numbers posted here

Answered By: Dima Tisnek

Just a quick example of numpy in action:

data = numpy.random.rand(1000000)

No need for loop, you can pass in how many numbers you want to generate.

Answered By: sedeh

If you have access to multiple cores, the computations can be done in parallel with dask.array:

import dask.array as da
x = da.random.random(size=(rows, cols)).compute()
# .compute is not necessary here, because calculations
# can continue in a lazy form and .compute is used
# on the final result
Answered By: SultanOrazbayev
import random
for i in range(1000000):
print(random.randint(1, 1000000))

Here’s a code in Python that you can use to generate one million random numbers, one per line!

Answered By: Saud Ilyas
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