Hello and welcome to the second part of my mini-series using cluster analysis in order to categorise formula 1 circuits. please go check the first part it outlines the basic data we are using to categorise the circuits and an overview of the method used for hierarchical clustering. Today we are going to go with K-means clustering.
For K-means clustering we have to set our own value for K we are going to do that with two different types of analysis. An elbow plot and silhouette analysis.
The code below is what was used in order to generate the elbow plot. The elbow plot generated is below:
Reviewing the elbow plot it looks like already we are seeing a slightly different amount of clusters then we got when we conducted hierarchical clustering. The elbow of the plot looks to be at 3 but you can also argue there is one at 4 as well as the value for k.
The other way to decide a k value when conducting k means clustering is to produce a silhouette graph. This takes every point which is part of the analysis and rates it on how it fits in with each cluster with -1 being doesn’t fit at all and 1 being fits well. You then produce a graph for each value of k with the average silhouette width and the highest point is the value of k. I have put a picture of the code below and also the silhouette graph produced
Fascinatingly there are two high points. One for a k of 9 and another for a k of 3. I am going to choose a k of 3 as this is closely aligned to what we saw in the elbow plot and 9 clusters are just too many to deal with.
The above graph shows all the circuits in the calendar and where they are for average straight length and average speed, colour by the cluster they have been put in. I am a bit unsatisfied with this. I feel this doesn’t quite fit the different circuits on the calendar. For instance, Singapore is different to China and Germany. Therefore K-means is not going to be the clustering I use in the final blog to look at pace trends across the season. Look out for the final blog which we will look at the pace across all circuits so far for all the teams and we will look at some other metrics like overtakes and pitstops.