Cd-hit contains a number of programs designed to quickly group sequences. cd-hit groups proteins into clusters that meet a user-defined similarity threshold. cd-hit-est is similar to cd-hit, but designed to group nucleotide sequences (without introns). cd-hit-est-2d is similar to cd-hit-2d but designed to compare two nucleotide datasets. A number of other related programs are also in this package. Please see the cd-hit user manual, also part of this package, for further information.