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How to you find the cumulative sum in Python?

Posted on April 19, 2021March 31, 2022 By Pythoneo

Let’s learn how to you find the cumulative sum in Python. We will use Numpy cumsum method for that.
python cumulative sum numpy cumsum

To calculate cumulative sum in Python you need to use Numpy cumsum method. Your array is the parameter which needs to be used. I created sample 3 x 3 array which I will sum up cumulatively.

import numpy as np

my_array = np.array([0, 20, 25, 40, 100, 300,
                     500, 800, 2000]).reshape(3, -1)
print(f"This is my array: \n {my_array}")
my_cumsum_array = np.cumsum(my_array)
print(f"This is the cumulative sum of my array"
      f":\n {my_cumsum_array}")

python cumulative sum numpy cumsum

As you can see Python summed every element up.

See also  How to resolve MemoryError: Unable to allocate array in Numpy?

How to create a cumulative sum column in python?

It is also a possibility to calculate cumulative sum for columns. You need to add axis parameters to cumsum method.

import numpy as np

my_array = np.array([0, 20, 25, 40, 100, 300,
                     500, 800, 2000]).reshape(3, -1)
print(f"This is my array: \n {my_array}")
my_cumsum_array = np.cumsum(my_array, axis=0)
print(f"This is the cumulative columns sum of my array"
      f":\n {my_cumsum_array}")

python cumulative column sum Numpy cumsum

Columns got sumed up.

See also  How to rotate a matrix with Numpy

How to create a cumulative sum row in python?

And now you can see the difference after changing axis value to 1. This is how to calculate cum sum for a row.

import numpy as np

my_array = np.array([0, 20, 25, 40, 100, 300,
                     500, 800, 2000]).reshape(3, -1)
print(f"This is my array: \n {my_array}")
my_cumsum_array = np.cumsum(my_array, axis=1)
print(f"This is the cumulative rows sum of my array"
      f":\n {my_cumsum_array}")

python cumulative rows sum Numpy cumsum

And this is how rows got summed up.

See also  How to Generate Sequence Arrays in Python with Numpy arange
numpy Tags:array, column, cumsum, rows, sum

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