PIG how to count a number of rows in alias
COUNT is part of pig see the manual
LOGS= LOAD 'log';LOGS_GROUP= GROUP LOGS ALL;LOG_COUNT = FOREACH LOGS_GROUP GENERATE COUNT(LOGS);
Arnon Rotem-Gal-Oz already answered this question a while ago, but I thought some may like this slightly more concise version.
LOGS = LOAD 'log';LOG_COUNT = FOREACH (GROUP LOGS ALL) GENERATE COUNT(LOGS);
Be careful, with COUNT your first item in the bag must not be null. Else you can use the function COUNT_STAR to count all rows.