sjc.elbow: Compute elbow values of a k-means cluster analysis
Description
Plot elbow values of a k-means cluster analysis. This function
computes a k-means cluster analysis on the provided data frame
and produces two plots: one with the different elbow values
and a second plot that maps the differences between each
"step" (i.e. between elbow values) on the y-axis. An
increase in the second plot may indicate the elbow criterion.