The Numpy library in Python comes with a number of useful built-in functions for computing common descriptive statistics like mean, median, standard deviation, etc. In this tutorial, we will look at how to get the median value of a Numpy array containing one or more NaN values.

## Can you use the `numpy.median()`

function on an array with NaN values?

We use the `numpy.median()`

function to get the median value of an array in Numpy. But what happens if the array contains one or more NaN values?

Let’s find out.

import numpy as np # create array ar = np.array([1, 2, np.nan, 3]) # get array median print(np.median(ar))

Output:

nan

Here, we created a one-dimensional Numpy array containing some numbers and a NaN value. We then applied the `numpy.median()`

function which resulted in `nan`

. This happened because the `numpy.median()`

function wasn’t able to handle the `nan`

value present in the array when computing the median.

Thus, you cannot use the `numpy.median()`

function to calculate the median of an array with NaN values.

## How to ignore NaN values when calculating the median of a Numpy array?

You can use the `numpy.nanmedian()`

function to calculate the median of a Numpy array containing NaN values. Pass the array as an argument.

The following is the syntax –

# median of array with nan values numpy.nanmedian(ar)

It returns the median value in the array ignoring all the NaN values.

Let’s look at some examples of using the `numpy.nanmedian()`

function.

### Example 1 – Median of one-dimensional array with NaN values

Let’s apply the `numpy.nanmedian()`

function on the same array used in the example above.

import numpy as np # create array ar = np.array([1, 2, np.nan, 3]) # get array median print(np.median(ar))

Output:

2.0

We get the median in the above array as 2.0. The `numpy.nanmedian()`

function ignores the NaN values when computing the median (2 is the median among 1, 2, 3).

### Example 2 – Median of multi-dimensional array with NaN values

The `numpy.nanmedian()`

function is very similar to the `numpy.median()`

function in its arguments. For example, use the `axis`

parameter to specify the axis along which to compute the median.

First, let’s create a 2-D Numpy array.

# create 2-D numpy array ar = np.array([[1, np.nan, 3], [np.nan, 5, np.nan]]) # display the array print(ar)

Output:

[[ 1. nan 3.] [nan 5. nan]]

Here, we used the `numpy.array()`

function to create a Numpy array with two rows and three columns. You can see that there are some NaN values present in the array.

If you use the Numpy `nanmedian()`

function on an array without specifying the axis, it will return the median of all the values inside the array.

# median of array print(np.nanmedian(ar))

Output:

3.0

We get the median of all the values inside the 2-D array.

Use the `numpy.nanmedian()`

function with `axis=1`

to get the median for each row in the array.

# median of each row in array print(np.nanmedian(ar, axis=1))

Output:

[2. 5.]

We get the median of each row in the above 2-D array. The median of values in the first row is (1+3)/2 = 2 and the median of values in the second row is 5 (since it’s the only non-NaN value in that row).

Use the `numpy.nanmedian()`

function with `axis=0`

to get the median of each column in the array.

# median of each column in array print(np.nanmedian(ar, axis=0))

Output:

[1. 5. 3.]

We get the median of each column in the above 2-D array. In this example, each column has one NaN value and one non-NaN value (which naturally becomes the median since it’s the only value in the column).

## Summary – Median of Numpy array with NaN values

The following is a short summary of the important points mentioned in this tutorial.

- Using the
`numpy.median()`

function on an array with NaN values results in NaN. - Use the
`numpy.nanmedian()`

function to get the median value in an array containing one or more NaN values. It computes the median by taking into account only the non-NaN values in the array. - Similar to the
`numpy.median()`

function, you can specify the axis along which you want to compute the median with the`numpy.nanmedian()`

function.

You might also be interested in –

- Get the Median of Numpy Array – (With Examples)
- Get the Mean of Numpy Array – (With Examples)
- Numpy – Get Standard Deviation of Array Values
- Extract the First N Elements of Numpy Array

**Subscribe to our newsletter for more informative guides and tutorials. ****We do not spam and you can opt out any time.**