What is compressed chemical clustering?

[MolSoft ICM Knowledge Base]

Question: 

What is compressed chemical clustering?

Answer:

When you make a cluster tree there is an option called compressed clustering and in some instances you might see it automatically activated. Clustering is a very memory intensive job and requires a  diagonal matrix of size (NxN) to be allocated. For example a table with 50K chemicals will require a matrix of the following size. (50K*50K*4)/2  = 5Gb (4 bytes per float number). The GUI automatically switches to 'compressed clustering' if the matrix the matrix size larger than 200Mb, but user can always manually pick full clustering option. The compressed clustering uses an approach similar to the Farthest-First Clustering method.