# Check if Value is NaN in Python

Home /

#### Related Tutorials

NaN stands for “Not a Number”. It is a special floating-point value that is used to represent the result of an undefined or unrepresentable mathematical operation.

NaN can arise in several ways, such as when dividing a number by zero, taking the square root of a negative number, or performing operations with infinity.

NaN is often used to indicate missing or undefined data in data analysis and scientific computing. In Python, NaN is represented by the special value ‘`float('nan')`‘ or ‘`numpy.nan`‘ when using the NumPy library.

It’s important to note that NaN values do not compare equal to any other value, including other NaN values. This means that a comparison such as ‘`NaN == NaN`‘ will always return ‘`False`‘. In Python, you can use the ‘`math.isnan()`‘ function to check whether a value is NaN or not.

### Check for NaN Values in Python

In Python, you can check for NaN values using the `math.isnan()` function or the NumPy library’s ‘`numpy.isnan()`function. Here are some examples:

Python
``````import math
import numpy as np

# Check if a value is NaN using math.isnan()
x = float('nan')
if math.isnan(x):
print('x is NaN')
else:
print('x is not NaN')

# Check if a value is NaN using numpy.isnan()
arr = np.array([1.0, float('nan'), 2.0, np.nan])
nan_indices = np.isnan(arr)
print(nan_indices)
``````

In the first example, `math.isnan()` is used to check whether the value of ‘`x`‘ is NaN. If ‘`x`‘ is NaN, the function returns ‘`True`‘ and the program prints `'x is NaN'`. Otherwise, the function returns ‘`False`” and the program prints `'x is not NaN'`.

In the second example, a NumPy array containing some NaN values is created. The `np.isnan()` function is used to check which elements of the array are NaN, returning a boolean array where ‘`True`‘ indicates a NaN value. This boolean array can be used to mask or filter the original array to work with only the non-NaN values.

Note that the ‘`==`‘ operator should not be used to check for NaN values, as it will always return ‘`False`‘ even when comparing NaN to itself.

## Fix NaN Value Problem

The approach to fixing NaN values depends on the specific problem and the nature of the data. However, here are some common techniques that can be used to address NaN values in Python:

1. Remove NaN values: If the NaN values are in a small proportion of the dataset and do not significantly affect the analysis, you can simply remove the rows or columns that contain NaN values. You can use the `pandas.DataFrame.dropna()` function to remove NaN values from a pandas DataFrame.
2. Fill NaN values with a constant: If the NaN values represent missing data, you can fill them with a constant value that is representative of the data. For example, you can fill NaN values with the mean, median, or mode of the non-NaN values in the column. You can use the ‘`pandas.DataFrame.fillna()`‘ function to fill NaN values in a pandas DataFrame.
3. Interpolate NaN values: If the NaN values represent missing data that has some level of predictability or correlation with the other data, you can interpolate the NaN values based on the adjacent non-NaN values. For example, you can use linear or polynomial interpolation to estimate the NaN values based on the surrounding data. You can use the ‘`pandas.DataFrame.interpolate()`‘ function to interpolate NaN values in a pandas DataFrame.
4. Use machine learning techniques: If the NaN values are part of a predictive modeling problem, you can use machine learning techniques to impute the missing values. For example, you can use regression models or neural networks to predict the missing values based on the other data in the dataset.

It’s important to note that filling or interpolating NaN values can potentially introduce bias or noise into the data, and should be done with caution. It’s also a good practice to carefully examine the data to understand the reasons for the NaN values and to choose an appropriate approach for handling them.