Groups are specified in a group file, which is a tabbed text file given by the -labels option. Each line in the group file must have two fields: the sample identifier and the group identifier. Some samples may be omitted, and a sample may appear in more than one group. For example, the following group file specifies two groups, mock and soil, each with three samples.
The output file is specified by the -output option. The output file is also in QIIME classic format.
usearch -otutab_group otutable.txt -labels groups.txt -output otutable_groups.txt