What is the algorithm behind GROUP USING 'collected' and 'merge'

Hi guys, Can anyone help me with this question: http://stackoverflow.com/questions/25097414/what-is-the-algorithm-behind-group-using-collected-and-merge

RANK in nested foreach, is it working?

Hi, can't make it work: flatRank = FOREACH groupedRecs { ranked = RANK recs by score DESC; filtered = FILTER ranked by $0 <100; GENERATE FLATTEN(ranked) as ($0 as rank_val, item_id, r_item_id, score); } Error: Syntax error, unexpected symbol at or near 'RANK'