Fig. 1.
Data set contains two clusters determined by two variables 
and 
such that points around 
and 
naturally form clusters. There are 200 observations (100 for each cluster) and 1,002 variables (
, 
and 1,000 random noise variables). We plot the data in the 2D space of 
and 
. Graphs with true cluster labels and predicted cluster labels obtained by clustering using only 
and 
and clustering by using all variables are laid from left to right. The predicted labels are the same as the true labels only when 
and 
are used for clustering; however, the performance is much worse when all variables are used.