I have a list of masks and I want to obtain the resulting mask by multiplying all of them. My Donkey Kong approach is the following:
a = [[1, 1], [1, 0], [1, 0]]
b = a[0]
for i in range(1, len(a)):
b = b * np.array(a[i])
which I think it works as returns [1,0]
as value of b
.
Is there a nicer way of doing this?
EDIT: I am looking for common ranges in the mask. To find all the non zero ranges I do the following: label = 0
for i in range(1, len(labels)):
label = label + np.array(labels[i])
label = [1 if x > 0 else 0 for x in label]
The zip() function in python can combine the contents of 2 or more iterables. Zip Function returns a zipped output. We can then simply store the output in Result and Display it on the console. This is a very simple way to perform list multiplication in Python.
We use the * operator to multiply the elements of the second list with respective elements of the nested list.
Lists and strings have a lot in common. They are both sequences and, like pythons, they get longer as you feed them. Like a string, we can concatenate and multiply a Python list.
Use a list comprehension to multiply each number in a range by specific number, e.g. result = [num * 2 for num in range(1, 6)] . The list comprehension iterates over the range and uses the multiplication * operator to multiply the current number by another number.
Take a look at np.prod, which returns the product of array elements over a given axis:
import numpy as np
a = [[1, 1], [1, 0], [1, 0]]
np.prod(a, axis=0)
I see that you are already using numpy so it can be used like other answers suggested. But still, a nice built-in solution only using reduce
can be:
from functools import reduce
a = [[1, 1], [1, 0], [1, 0]]
def element_wise_multiply(list1, list2):
return [x*y for x,y in zip(list1, list2)]
b = reduce(element_wise_multiply, a)
# Or as a lambda:
b = reduce(lambda list1, list2: [x*y for x,y in zip(list1, list2)], a)
This takes every two sub-lists and reduces them to one by multiplying all index-matching elements by using zip
. It also gives:
[1, 0]
Use np.prod
:
>>> np.prod(a, axis=0)
array([1, 0])
>>>
Or you could use np.cumprod
and get the last value:
>>> np.cumprod(a, axis=1)[-1]
array([1, 0], dtype=int32)
>>>
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