Gist 737033

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✓ Published0🌍 Public

Last edited Dec 11, 2010

Created on Dec 11, 2010

This example demonstrates a MapReduce aggregation over a MongoDB collection of crime records, showing the count of crimes grouped by property name. The code first seeds a `crimes` collection with sample data, then defines a `map` function that emits each property name with a value of 1, and a `reduce` function that sums the emitted values. The MapReduce operation runs via `db.crimes.mapReduce()` and outputs the results as a JSON array using `printjson`. It uses MongoDB’s JavaScript shell API for data insertion, mapping, reduction, and result retrieval.

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