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db.things.find() { "_id" : 1, "tags" : [ "dog", "cat" ] } { "_id" : 2, "tags" : [ "cat" ] } { "_id" : 3, "tags" : [ "mouse", "cat", "dog" ] } m = function () { this.tags.forEach(function (z) { //统计前过滤 if(z == 'dog'){ emit(z, {count:1}); } }); } f=function (key, values) { var result = {count:0}; values.forEach(function (value) {result.count += value.count;}); return result; } m = function () { emit(actionType, {count:1}); } f=function (key, values) { var result = {count:0}; values.forEach(function (value) {result.count += value.count;}); return result; } res = db.things.mapReduce(m, f, {out: {replace: "test_result"}}); http://www.faithbee.com/?p=180

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