Qfyilyi

I have around 40k rows and I want to test all kinds of selection combinations on the rows. By selection I mean boolean masks. The number of masks/filters is around 250MM.

The current simplified code:

np_arr = np.random.randint(1, 40000, 40000)

results = np.empty(250000000)

filters = np.random.randint(1, size=(250000000, 40000))

for i in range(250000000):

    row_selection = np_arr[filters[i].astype(np.bool_)] # Select rows based on next filter

    # Performing simple calculations such as sum, prod, count on selected rows and saving to result

    results[i] = row_selection.sum() # Save simple calculation result to results array

I tried Numba and Multiprocessing, but since most of the processing is in the filter selection rather than the computation, that doesn't help much.

What would be the most efficient way to solve this? Is there any way to parallelize this? As far as I see I need to loop through each filter to then individually calculate the sum, prod, count etc because I can't apply filters in parallel (even though the calculations after applying the filters are very simple).

Appreciate any suggestions on performance improvement/speedup.

To get good performane within Numba simply avoid masking and therefore very costly array copies. You have to implement the filters yourself, but that shouldn't be any problem with the filters you mentioned.

Parallelization is also very easy to do.

Example

import numpy as np

import numba as nb



max_num = 250000 #250000000

max_num2 = 4000#40000

np_arr = np.random.randint(1, max_num2, max_num2)

filters = np.random.randint(low=0,high=2, size=(max_num, max_num2)).astype(np.bool_)



#Implement your functions like this, avoid masking

#Sum Filter

@nb.njit(fastmath=True)

def sum_filter(filter,arr):

  sum=0.

  for i in range(filter.shape[0]):

    if filter[i]==True:

      sum+=arr[i]

  return sum



#Implement your functions like this, avoid masking

#Prod Filter

@nb.njit(fastmath=True)

def prod_filter(filter,arr):

  prod=1.

  for i in range(filter.shape[0]):

    if filter[i]==True:

      prod*=arr[i]

  return sum



@nb.njit(parallel=True)

def main_func(np_arr,filters):

  results = np.empty(filters.shape[0])

  for i in nb.prange(max_num):

    results[i]=sum_filter(filters[i],np_arr)

    #results[i]=prod_filter(filters[i],np_arr)

  return results

One way to improve is to move the as_type outside the loop. In my tests it reduced the execution time by more than half.
For comparison, check the two codes below:

import numpy as np

import time



max_num = 250000 #250000000

max_num2 = 4000#40000

np_arr = np.random.randint(1, max_num2, max_num2)

results = np.empty(max_num)

filters = np.random.randint(1, size=(max_num, max_num2))

start = time.time()

for i in range(max_num):

    row_selection = np_arr[filters[i].astype(np.bool_)] # Select rows based on next filter

    # Performing simple calculations such as sum, prod, count on selected rows and saving to result

    results[i] = row_selection.sum() # Save simple calculation result to results array



end = time.time()

print(end - start)

takes 2.12

while

import numpy as np

import time



max_num = 250000 #250000000

max_num2 = 4000#40000

np_arr = np.random.randint(1, max_num2, max_num2)

results = np.empty(max_num)

filters = np.random.randint(1, size=(max_num, max_num2)).astype(np.bool_)

start = time.time()

for i in range(max_num):

    row_selection = np_arr[filters[i]] # Select rows based on next filter

    # Performing simple calculations such as sum, prod, count on selected rows and saving to result

    results[i] = row_selection.sum() # Save simple calculation result to results array



end = time.time()

print(end - start)

takes 0.940