# Calculate the sum of all columns in a 2D NumPy array

• Last Updated : 21 Jul, 2021

Let us see how to calculate the sum of all the columns in a 2D NumPy array.
Method 1 : Using a nested loop to access the array elements column-wise and then storing their sum in a variable and then printing it.
Example 1:

## Python3

 `# importing required libraries``import` `numpy` `# explicit function to compute column wise sum``def` `colsum(arr, n, m):``    ``for` `i ``in` `range``(n):``        ``su ``=` `0``;``        ``for` `j ``in` `range``(m):``            ``su ``+``=` `arr[j][i]``        ``print``(su, end ``=` `" "``)   ` `# creating the 2D Array``TwoDList ``=` `[[``1``, ``2``, ``3``], [``4``, ``5``, ``6``],``            ``[``7``, ``8``, ``9``], [``10``, ``11``, ``12``]]``TwoDArray ``=` `numpy.array(TwoDList)` `# displaying the 2D Array``print``(``"2D Array:"``)``print``(TwoDArray)` `# printing the sum of each column``print``(``"\nColumn-wise Sum:"``)``colsum(TwoDArray, ``len``(TwoDArray[``0``]), ``len``(TwoDArray))`

Output :

```2D Array:
[[ 1  2  3]
[ 4  5  6]
[ 7  8  9]
[10 11 12]]

Column-wise Sum:
22 26 30 ```

Example 2 :

## Python3

 `# importing required libraries``import` `numpy` `# explicit function to compute column wise sum``def` `colsum(arr, n, m):``    ``for` `i ``in` `range``(n):``        ``su ``=` `0``;``        ``for` `j ``in` `range``(m):``            ``su ``+``=` `arr[j][i]``        ``print``(su, end ``=` `" "``)   ` `# creating the 2D Array``TwoDList ``=` `[[``1.2``, ``2.3``], [``3.4``, ``4.5``]]``TwoDArray ``=` `numpy.array(TwoDList)` `# displaying the 2D Array``print``(``"2D Array:"``)``print``(TwoDArray)` `# printing the sum of each column``print``(``"\nColumn-wise Sum:"``)``colsum(TwoDArray, ``len``(TwoDArray[``0``]), ``len``(TwoDArray))`

Output :

```2D Array:
[[1.2 2.3]
[3.4 4.5]]

Column-wise Sum:
4.6 6.8 ```

Method 2: Using the sum() function in NumPy, numpy.sum(arr, axis, dtype, out) function returns the sum of array elements over the specified axis. To compute the sum of all columns the axis argument should be 0 in sum() function.
Example 1 :

## Python3

 `# importing required libraries``import` `numpy` `# creating the 2D Array``TwoDList ``=` `[[``1``, ``2``, ``3``], [``4``, ``5``, ``6``],``            ``[``7``, ``8``, ``9``], [``10``, ``11``, ``12``]]``TwoDArray ``=` `numpy.array(TwoDList)` `# displaying the 2D Array``print``(``"2D Array:"``)``print``(TwoDArray)` `# printing the sum of each column``print``(``"\nColumn-wise Sum:"``)``print``(numpy.``sum``(TwoDArray, axis ``=` `0``))`

Output :

```2D Array:
[[ 1  2  3]
[ 4  5  6]
[ 7  8  9]
[10 11 12]]

Column-wise Sum:
22 26 30```

Example 2 :

## Python3

 `# importing required libraries``import` `numpy` `# creating the 2D Array``TwoDList ``=``[[``1.2``, ``2.3``], [``3.4``, ``4.5``]]``TwoDArray ``=` `numpy.array(TwoDList)` `# displaying the 2D Array``print``(``"2D Array:"``)``print``(TwoDArray)` `# printing the sum of each column``print``(``"\nColumn-wise Sum:"``)``print``(``*``numpy.``sum``(TwoDArray, axis ``=` `0``))`

Output :

```2D Array:
[[1.2 2.3]
[3.4 4.5]]

Column-wise Sum:
4.6 6.8```

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