How to Check Seasonality in a Time Series Using Python

Time series analysis is a powerful tool that is often overlooked in data analysis. It deals with the analysis of order, often time-based data.

One of the fundamental aspects of time series analysis is the understanding of seasonality – the recurring patterns observable in predictable, consistent intervals over time.

This tutorial will guide you through the steps of using Python to identify seasonality in time series data.

Step 1: Import the necessary libraries

We will be using the pandas, matplotlib, and statsmodels libraries in Python. If these libraries are not installed in your Python environment, you can install them using pip.

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pip install pandas matplotlib statsmodels seaborn

Step 2: Loading your time series data

Using pandas, we load into a DataFrame the time series data that we want to analyze. In our example, we will use simple time series data which will allow us to illustrate the concept in a clear manner.

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import pandas as pd
df = pd.read_csv('data.csv')
 
Date,Value
2023-01-01,10
2023-01-02,12
2023-01-03,15
2023-01-04,18
2023-01-05,20
2023-01-06,22
2023-01-07,25
2023-01-08,28
2023-01-09,30
2023-01-10,33

Please populate the data.csv file with your respective time series data.

Step 3: Visualizing the time series data

Before moving to any computations or testing, it’s always a good idea to visualize your data first. We’ll use the matplotlib and seaborn libraries to plot our time series data.

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import matplotlib.pyplot as plt
import seaborn as sns
 
plt.figure(figsize=(10,6))
sns.lineplot(data=df)
plt.show()

Step 4: Check for seasonality using Seasonal Decompose

One of the methods to check for seasonality is using the seasonal decompose in statsmodels. This function decomposes our time series into three distinct components: trend, seasonality, and noise.

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from statsmodels.tsa.seasonal import seasonal_decompose
 
result = seasonal_decompose(df, model='multiplicative')
result.plot()
plt.show()

The seasonal plot shows the data’s seasonality component while the residual plot shows an irregular component (anything left over from the trend and seasonal part).

Full Code

If you’ve followed along, your full code should look like this:

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import pandas as pd
import matplotlib.pyplot as plt
import seaborn as sns
from statsmodels.tsa.seasonal import seasonal_decompose
 
df = pd.read_csv('data.csv')
 
plt.figure(figsize=(10,6))
sns.lineplot(data=df)
plt.show()
 
result = seasonal_decompose(df, model='multiplicative')
result.plot()
plt.show()

Conclusion

That’s it! You’ve successfully completed a basic analysis of the seasonality of a time series in Python! While this process isn’t exhaustive, it’s a solid starting point. Always look to learn more about time series, there are several other techniques to determine and adjust for seasonality.