I can't think of a nice one but you could first sort your data then generate a sequence number for each row (use Numeric.sequence("sequencename",1,1)) and temporarily store the flow (using tFileOutput or tHashOutput). Then read back the stored rows to retrieve the value from the count/2 row (either read only that many rows and then use the last function in tAggregateRow or use a tJavaRow to store the value only when the sequence number equals count/2; get the count from the NB_LINE globalMap variable of your output component).