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How to Visualize Anomalies in Time Series Data in R, with ggplot

Quickly see what’s below and above average through the noise and seasonal trends.

Whether or not values in a time series are normal or abnormal can be tricky to show because of underlying trends and periodic cycles in the data. One technique to visualize this aspect of time series data is to visualize the normal values, and plot the deviations from those normal values (sometimes called “anomalies”) on top of those.

This technique applies especially well to weather data. In order to show how normal or abnormal cold and hot weather spells are, plotting the raw numbers is usually not very interesting: it is much more meaningful to plot the deviations from the normal values to see if a spell is unusually hot or cold for the time of the year.

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About the Author

Maarten is a data journalist and data visualization consultant from Belgium. He likes maps, ggplot and a good story.