CODEWITHSUNDEEP
pythonarraysnumpy
MaxPowers
MaxPowers

Reputation: 5486

Assign a list of values to a numpy array

Suppose there is a 2-dimensional numpy array of shape (10000, 100) and size 1000000. There is also a 1-dimensional list of length 1000000. What would be the fastest way to assign all the values in the list to the array? My solution is:

my_array = np.zeros([10000, 100]) 
my_list = range(1000000)
length_of_list = len(my_list)

for i in range(length_of_list):                  
    my_array.flat[i] = my_list[i]

Is there maybe a better one?

Upvotes: 1

Views: 6402

Answers (1)

Andrey Sobolev
Andrey Sobolev

Reputation: 12683

I thought that turning the list to an array and reshaping it then would be the fastest solution, but it turned out in my setup @M4rtini's one-liner is even faster:

In [25]: %%timeit -n 10 
   ....: for i in range(length_of_list):                  
   ....:     my_array.flat[i] = my_list[i]
   ....: 
10 loops, best of 3: 420 ms per loop

In [26]: %timeit -n 10 my_array.flat[:] = my_list
10 loops, best of 3: 119 ms per loop

In [27]: %timeit -n 10 my_array = np.array(my_list).reshape(10000, 100)
10 loops, best of 3: 133 ms per loop

Upvotes: 3

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