Is there a method in numpy to multiply every element in an array?

问题

I want to multiply all elements in a numpy array. If there's an array like [1,2,3,4,5], I want to get value of 1*2*3*4*5.

I tried this by making my own method, but size of array is very large, it takes very longs time to calculate because I'm using numpy it would be helpful if numpy supports this operation.

I tried to find out through numpy documents, but I failed. Is there a method which does this operation? If there is, is there a way to get values along a rank in an matrix?

回答1:

I believe what you need is, numpy.prod.

From the documentation:

Examples

By default, calculate the product of all elements:

>>> np.prod([1.,2.])
2.0

Even when the input array is two-dimensional:

>>> np.prod([[1.,2.],[3.,4.]])
24.0

But we can also specify the axis over which to multiply:

>>> np.prod([[1.,2.],[3.,4.]], axis=1)
array([  2.,  12.])

---

So for your case, you need:

>>> np.prod([1,2,3,4,5])
120

回答2:

You can use something like this:

import numpy as np
my_array = np.array([1,2,3,4,5])
result = np.prod(my_array)
#Prints 1*2*3*4*5
print(result)

Here is the documentation of numpy.prod
Below is a excerpt from the link above:

By default, calculate the product of all elements:

>>> np.prod([1.,2.])
2.0

Even when the input array is two-dimensional:

>>> np.prod([[1.,2.],[3.,4.]])
24.0

But we can also specify the axis over which to multiply:

>>> np.prod([[1.,2.],[3.,4.]], axis=1)
array([  2.,  12.])

来源：https://stackoverflow.com/questions/44212854/is-there-a-method-in-numpy-to-multiply-every-element-in-an-array