Time-series data segmentation.
In the last post, we found that the sales has a seasonal trend. In this post, I'd like to see the detail of the trend. When we see the seasonal trend (Blue line), it looks that there are peaks in September, November and December. We can assume that there were promotions in those periods or other events. As you can imagine, sales condition can be changed. The goal is this post is to see how to catch the "Change" with some methods. The purpose is to catch the change is because