{"id":652,"date":"2012-03-23T13:24:17","date_gmt":"2012-03-23T05:24:17","guid":{"rendered":"https:\/\/yanjingang.com\/blog\/?p=652"},"modified":"2016-03-10T13:24:52","modified_gmt":"2016-03-10T05:24:52","slug":"mongodb-group-by-mapreduce","status":"publish","type":"post","link":"https:\/\/yanjingang.com\/blog\/?p=652","title":{"rendered":"mongodb group by mapreduce"},"content":{"rendered":"

\u65b0\u5efacollection <\/span>\u540d\u79f0\u00a0\u00a0\u00a0test <\/span>\uff0c\u8868\u4e2d\u7684\u5185\u5bb9
\nmongos> db.test.find();
\n{ “_id” : ObjectId(“4ee7125f0f3210cf35a32f02″),”name” : “xm01”, “age” : 10 }
\n{ “_id” : ObjectId(“4ee712a80f3210cf35a32f03″),”name” : “xm02”, “age” : 20 }
\n{ “_id” : ObjectId(“4ee712c60f3210cf35a32f04″),”name” : “xm01”, “age” : 30 }
\n{ “_id” : ObjectId(“4ee712d20f3210cf35a32f05″),”name” : “xm02”, “age” : 20 }
\n{ “_id” : ObjectId(“4ee712d70f3210cf35a32f06″),”name” : “xm03”, “age” : 20 }
\n{ “_id” : ObjectId(“4ee7173d0f3210cf35a32f07″),”name” : “xm02”, “age” : 10 }<\/p>\n

<\/span>\u4e0b\u9762\u5bf9name<\/span>\u505agroup by ,<\/span>\u5bf9age<\/span>\u505a\u6c47\u603b
\n<\/span>\u5b9a\u4e49 map<\/span>\u51fd\u6570
\nm=function(){emit(this.name,{age:this.age})}; \/\/<\/span>\u7edf\u8ba1name<\/span>\u6b21\u6570\uff1aemit(this.name,{cnt:1})
\n<\/span>\u5b9a\u4e49reduce<\/span>\u51fd\u6570
\nr=function(key,values){var result={age:0}; values.forEach(function(v){result.age +=v.age; } ); return result};
\n<\/span>\u8c03\u7528mapreduce<\/span>\u6267\u884cgroup by<\/span>\u67e5\u8be2
\nmongos> db.runCommand({
\n… mapreduce:”test”,\u00a0\u00a0\u00a0\u00a0 \/\/<\/span>\u6267\u884c\u5206\u7ec4\u7684\u96c6\u5408
\n…map:m,\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\/\/map<\/span>\u51fd\u6570\uff0c\u5faa\u73af\u96c6\u5408\u5bf9\u8c61
\n…reduce:r,\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\/\/reduce<\/span>\u51fd\u6570\uff0c\u5bf9document<\/span>\u505a\u6c47\u603b
\n…out:”res”\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\/\/<\/span>\u8f93\u51fa\u7ed3\u679c
\n… })
\n<\/span>\u7ed3\u679c\u663e\u793a\uff1a
\ndb.res.find();
\nmongos> db.res.find();
\n{ “_id” : “xm01”, “value” : { “count” :2, “age” : 40 } }
\n{ “_id” : “xm02”, “value” : { “count” :3, “age” : 50 } }
\n{ “_id” : “xm03”, “value” : { “count” :1, “age” : 20 } }<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

\u65b0\u5efacollection \u540d\u79f0\u00a0\u00a0\u00a0test \uff0c\u8868\u4e2d\u7684\u5185\u5bb9 mongos> db.test.find() […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[21],"tags":[338,22],"_links":{"self":[{"href":"https:\/\/yanjingang.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/652"}],"collection":[{"href":"https:\/\/yanjingang.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/yanjingang.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/yanjingang.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/yanjingang.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=652"}],"version-history":[{"count":0,"href":"https:\/\/yanjingang.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/652\/revisions"}],"wp:attachment":[{"href":"https:\/\/yanjingang.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=652"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/yanjingang.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=652"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/yanjingang.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=652"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}