September 19, 2021    /    Viewed: 166    /    Comments: 0    /    Edit

Examples of how to calculate the sum along an axis with numpy in python:

### Create a random matrix with numpy

Let's create a random matrix with numpy of size = (3,3):

````import numpy as np`

`data = np.random.randint(0,5,size=(3,3))`
```

returns for example

````array([[4, 1, 2],`
`             [2, 1, 1],`
`             [4, 0, 1]])`
```

### Sum along the first axis (axis=0)

To sum along a given axis of a matrix with numpy, a solution is to use numpy.sum with the parameter "axis":

````data.sum(axis=0)`
```

gives

````array([10,  2,  4])`
```

### Sum along the second axis (axis=1)

Another example along the axis=1

````data.sum(axis=1)`
```

gives

````array([7, 4, 5])`
```

### Sum all elements of a matrix with numpy

Note: to sum all elements of a matrix with numpy:

````data.sum()`
```

gives here

````16`
```

### Another example with more than 2 dimensions

Another example with a matrix of size = (3,3,3)

````import numpy as np`

`data = np.random.randint(0,5,size=(3,3,3))`
```

gives gor example

````array([[[4, 2, 4],`
`        [3, 3, 1],`
`        [0, 4, 1]],`

`       [[3, 4, 0],`
`        [3, 1, 3],`
`        [4, 4, 2]],`

`       [[2, 0, 2],`
`        [2, 4, 1],`
`        [3, 3, 4]]])`
```

Sum along axis=0

````data.sum(axis=0)`
```

gives

````array([[ 9,  6,  6],`
`             [ 8,  8,  5],`
`             [ 7, 11,  7]])`
```

Sum along axis=1

````data.sum(axis=1)`
```

gives

````array([[ 7,  9,  6],`
`       [10,  9,  5],`
`       [ 7,  7,  7]])`
```

Sum along axis=2

````data.sum(axis=2)`
```

gives

````array([[10,  7,  5],`
`       [ 7,  7, 10],`
`       [ 4,  7, 10]])`
```  ##### Daidalos

Hi, I am Ben.

I have developed this web site from scratch with Django to share with everyone my notes. If you have any ideas or suggestions to improve the site, let me know ! (you can contact me using the form in the welcome page). Thanks!