mongodb mapreduce学习
for( var i = 1; i < 10001; i++){
db.students.insert({classid:i%400, age:i%100, name:'Tom'+i})
}
db.students.insert({classid:1, age:14, name:'Tom'})
db.students.insert({classid:1, age:12, name:'Jacky'})
db.students.insert({classid:2, age:16, name:'Lily'})
db.students.insert({classid:2, age:9, name:'Tony'})
db.students.insert({classid:2, age:19, name:'Harry'})
db.students.insert({classid:2, age:13, name:'Vincent'})
db.students.insert({classid:1, age:14, name:'Bill'})
db.students.insert({classid:2, age:17, name:'Bruce'})
m = function() {
emit(this.classid, 1)
}
r = function(key, values) {
var x = 0;
values.forEach(
function(v) { x += v }
);
return x;
}
res = db.runCommand({
mapreduce:"students",
map:m,
reduce:r,
out:"students_res"
});
db.students_res.find()
m = function() {
emit(this.classid, {cnt:1,name:this.name})
}
r = function(key, values) {
var x = 0;
var names="";
values.forEach(
function(v)
{
x += v.cnt;
names+=v.name;
}
);
return {classid:key,cnt:x,names:names};
}
res = db.runCommand({
mapreduce:"students",
map:m,
reduce:r,
out:"students_res"
});
db.students_res.find()
f = function(key, value) { return {classid:key, count:value}; }
res = db.runCommand({
mapreduce:"students",
map:m,
reduce:r,
out:"students_res",
finalize:f
});
db.students_res.find()
res = db.runCommand({
mapreduce:"students",
map:m,
reduce:r,
out:"students_res",
finalize:f,
query:{age:{$lt:10}}
});
db.students_res.find()
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