Pandas DataFrame Diff Method

Introduction

The Pandas DataFrame.diff() method calculates the difference between elements in a DataFrame. It provides the first discrete difference of elements, calculating the difference of a DataFrame element compared with another element in the DataFrame. By default, the method calculates the difference with the previous element in the row.

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Import the necessary libraries

To use the DataFrame.diff() method, we first need to import the pandas library:

import pandas as pd

Create a DataFrame

Next, let's create a DataFrame that we can use for the examples:

df = pd.DataFrame({'a': [1, 3, 8],'b': [3, 5, 8],'c': [16, 25, 36]})

Our DataFrame has three columns ('a', 'b', 'c') and three rows.

Calculate the difference with the previous row

To calculate the difference with the previous row, we can simply call the diff() method on our DataFrame:

diff_previous_row = df.diff()

This will calculate the difference between each element and the previous element in the row.

Calculate the difference between previous columns

If we want to calculate the difference between previous columns instead of previous rows, we can specify the axis parameter as 1:

diff_previous_column = df.diff(axis=1)

This will calculate the difference between each element and the previous element in the column.

Calculate the difference with a specific previous row

We can also calculate the difference with a specific previous row by specifying the periods parameter. For example, to calculate the difference with the second previous row, we can set periods to 2:

diff_second_previous_row = df.diff(periods=2)

This will calculate the difference between each element and the element two rows before.

Calculate the difference with a specific previous column

Similarly, we can calculate the difference with a specific previous column by specifying the periods and axis parameters. For example, to calculate the difference with the third previous column, we can set periods to 3 and axis to 1:

diff_third_previous_column = df.diff(periods=3, axis=1)

This will calculate the difference between each element and the element three columns before.

Summary

The DataFrame.diff() method in Pandas allows us to calculate the difference between elements in a DataFrame. We can calculate the difference with previous rows or previous columns, as well as with specific previous rows or columns. This method is useful when analyzing time series data or when comparing values between consecutive rows or columns. By using the diff() method, we can easily compute the changes or differences in our DataFrame.