{"id":"mr-groupby-requires-presort","text":"`_run_reducer` sorts all intermediate pairs by key before calling `itertools.groupby`, which is required because `groupby` only groups consecutive elements with the same key.","truth_value":"IN","source":"entries/2026/05/29/mapreduce-framework-mapreduce.md","source_url":"","source_hash":"","justifications":[],"dependents":[],"metadata":{},"explanation":{"steps":[{"node":"mr-groupby-requires-presort","truth_value":"IN","reason":"premise"}]}}