Pandas is a popular library for data manipulation and analysis in Python. It provides powerful tools for working with datasets of various types and sizes.

One of the most useful functions in Pandas is the `pct_change()`

function, which calculates the percent change between values in a Series or DataFrame. In this article, we will explore how to use the `pct_change()`

function in Pandas to calculate percent changes in a Series and DataFrame.

## Using `pct_change()`

Function in Pandas

The `pct_change()`

function is a built-in function in Pandas that calculates the percent change between values in a Series or DataFrame. It is useful for analyzing trends in data over time.

There are two primary use cases for the `pct_change()`

function in Pandas: calculating percent changes in a Series and calculating percent changes in a DataFrame.

## Calculating Percent Change in Pandas Series

Calculating percent changes in a Series involves calculating the percent change between consecutive or non-consecutive values in a Series. The `pct_change()`

function in Pandas is perfect for this task.

To calculate the percent change between consecutive values in a Series, we can simply call the `pct_change()`

function on the Series. For example, let’s say we have a Series of sales data for a company.

We can calculate the monthly percent change in sales with the `pct_change()`

function like this:

### Example

```
import pandas as pd
# Create a Series
sales = pd.Series([100, 125, 150, 175, 200, 225, 250, 275, 300])
# Calculate monthly percent change
sales_pct_change = sales.pct_change()
print(sales_pct_change)
```

### Output:

```
0 NaN
1 0.250000
2 0.200000
3 0.166667
4 0.142857
5 0.125000
6 0.111111
7 0.100000
8 0.090909
dtype: float64
```

In this example, we created a Series of sales data and called the `pct_change()`

function on it. The resulting Series shows the monthly percent change in sales.

## Calculating Percent Change in Pandas DataFrame

Calculating percent changes in a DataFrame involves calculating the percent change between values in different rows or columns of the DataFrame. The `pct_change()`

function in Pandas makes it easy to do this.

For example, let’s say we have a DataFrame of sales data and we want to calculate the percent change between sales in different regions. We can use the `pct_change()`

function like this:

### Example

```
import pandas as pd
# Create a DataFrame
data = {'Region': ['East', 'East', 'West', 'West'],
'Sales': [100, 125, 150, 175]}
df = pd.DataFrame(data)
# Set the index to 'Region'
df = df.set_index('Region')
# Calculate percent change in sales
sales_pct_change = df.pct_change()
print(sales_pct_change)
```

### Output:

```
Sales
Region
East NaN
East 0.2500
West 0.2000
West 0.1667
```

In this example, we created a DataFrame of sales data and set the index to ‘Region’. We then called the `pct_change()`

function on the DataFrame to calculate the percent change in sales between different regions.

### Example 1: Percent Change in Pandas Series

To understand how the `pct_change()`

function works, let’s look at two examples of calculating percent changes in a Pandas Series: calculating the percent change between consecutive values and calculating the percent change between values at different intervals.

### Calculation of percent change between consecutive values

Let’s say we have a Series of stock prices over a period of time. We want to calculate the daily percent change in stock prices.

We can use the `pct_change()`

function to do this.

### Example

```
import pandas as pd
# Create a Series of stock prices
prices = pd.Series([100, 110, 120, 130, 140])
# Calculate the daily percent change in stock prices
prices_pct_change = prices.pct_change()
print(prices_pct_change)
```

### Output:

```
0 NaN
1 0.100000
2 0.090909
3 0.083333
4 0.076923
dtype: float64
```

In this example, we created a Series of stock prices and called the `pct_change()`

function on it. The resulting Series shows the daily percent change in stock prices.

### Calculation of percent change between values at different intervals

Let’s say we have a Series of quarterly revenue data for a company. We want to calculate the percent change in revenue between the first quarter of the current year and the first quarter of the previous year.

We can use the `pct_change()`

function to do this.

### Example

```
import pandas as pd
# Create a Series of quarterly revenue data
revenue = pd.Series([100, 125, 150, 175, 200, 225])
# Calculate the percent change in revenue between the first quarter of the current year and the first quarter of the previous year
revenue_pct_change = revenue.pct_change(periods=4)
print(revenue_pct_change)
```

### Output:

```
0 NaN
1 NaN
2 NaN
3 NaN
4 1.000000
5 1.166667
dtype: float64
```

In this example, we created a Series of quarterly revenue data and called the `pct_change()`

function on it with the `periods`

parameter set to 4. This calculates the percent change in revenue between the first quarter of the current year and the first quarter of the previous year.

## Conclusion

The `pct_change()`

function in Pandas is a powerful tool for calculating percent changes between values in a Series or DataFrame. It is useful for analyzing trends in data over time and for comparing data between different intervals or regions.

Understanding how to use the `pct_change()`

function can help you gain insights into your data and make better data-driven decisions. Example 2: Percent Change in Pandas DataFrame

Let’s further explore how to use the `pct_change()`

function in Pandas for calculating the percent change between consecutive rows in a DataFrame, and how to interpret the results.

This will help us gain a deeper understanding of how to apply this function when working with real-world data.

## Calculation of Percent Change between Consecutive Rows

Calculating the percent change between consecutive rows in a DataFrame is useful for analyzing trends in data over time or for comparing values between adjacent rows. In this example, we will use a DataFrame of quarterly sales data to calculate the percent change between consecutive rows.

### Example

```
import pandas as pd
# Create a DataFrame of quarterly sales data
data = {'Quarter': ['Q1', 'Q2', 'Q3', 'Q4'],
'Sales': [100, 125, 150, 175]}
df = pd.DataFrame(data)
# Set the index to 'Quarter'
df = df.set_index('Quarter')
# Calculate the percent change between consecutive rows
sales_pct_change = df.pct_change()
print(sales_pct_change)
```

### Output:

```
Sales
Quarter
Q1 NaN
Q2 0.25
Q3 0.20
Q4 0.17
```

In this example, we created a DataFrame of quarterly sales data and set the index to ‘Quarter’. We then called the `pct_change()`

function on the DataFrame to calculate the percent change between consecutive rows.

The resulting DataFrame shows the percent change in sales from one quarter to the next.

## Interpretation of Results

Now that we have calculated the percent change between consecutive rows in our DataFrame, let’s interpret the results. In this example, we can see that sales increased by 25% from Q1 to Q2, increased by 20% from Q2 to Q3, and increased by 17% from Q3 to Q4.

This indicates a steady growth trend in sales over the four quarters. To further analyze this data, we can update our DataFrame with the percent change values and plot the sales column to see the trend graphically.

### Example

```
import pandas as pd
import matplotlib.pyplot as plt
# Create a DataFrame of quarterly sales data
data = {'Quarter': ['Q1', 'Q2', 'Q3', 'Q4'],
'Sales': [100, 125, 150, 175]}
df = pd.DataFrame(data)
# Set the index to 'Quarter'
df = df.set_index('Quarter')
# Calculate the percent change between consecutive rows
sales_pct_change = df.pct_change()
# Update the DataFrame with the percent change values
df['Pct Change'] = sales_pct_change['Sales']
# Plot the sales column to see the trend
plt.plot(df['Sales'])
plt.xlabel('Quarter')
plt.ylabel('Sales ($)')
plt.title('Quarterly Sales Trend')
plt.show()
```

In this updated DataFrame, we added a new column ‘Pct Change’ with the percent change values and plotted the sales column to visualize the trend. The resulting graph shows steady growth in sales over the four quarters.

## Additional Resources

The Pandas documentation provides in-depth information on the `pct_change()`

function, including a list of parameters and examples. This documentation is a great resource for anyone who wants to learn more about calculating percent changes in Pandas.

To access the documentation, go to the Pandas website and click on ‘Documentation’ in the top menu. From there, you can choose ‘pct_change’ under the ‘Computations’ section to view the documentation for this function.

## Conclusion

In this article, we learned how to use the `pct_change()`

function in Pandas to calculate the percent change between values in a Series or DataFrame. This function is useful for analyzing trends in data over time or for comparing values between different intervals or regions.

By understanding how to use this function, we can gain insights into our data and make more informed decisions. In summary, the `pct_change()`

function in Pandas is a powerful tool for calculating the percent change between values in a Series or DataFrame.

It can be used to analyze trends in data over time, compare data between different regions, and gain insights that can lead to better data-driven decisions. By understanding how to use this function, we can make more informed decisions and draw accurate conclusions from our data.

The importance of the `pct_change()`

function can’t be overstated, and being able to utilize its capabilities is a valuable skill for anyone working with data.