The data set SHIRTS contains the sizes of a particular shirt sold during a week at a clothing store, one observation for each shirt sold. 
data shirts;
   input Size $ @@;
   datalines;
medium    large
large     large
large     medium
medium    small
small     medium
medium    large
small     medium
large     large
large     small
medium    medium
medium    medium
medium    large
small     small
;