conn = new Mongo();
db = conn.getDB("db-name");  //选择数据库
db.auth("user-name","password");  //用户验证

var map = function() {
    split_result = this.sentence.split(" ");
    for (var i in split_result) {
        var word = split_result[i].replace(/(^\s*)|(\s*$)/g,"").toLowerCase(); //去除了单词两边可能的空格，并将单词转换为小写
        if (word.length != 0) {
            emit(word, 1);
        }
    }
}

var reduce = function(key, values) {
    print(key+":"+Array.sum(values));
    return Array.sum(values);
}

db.data.mapReduce(
    map,
    reduce,
    {out:{merge:"mr_result"}}
)

$ mongo test01.js

db.mr_result.find();

conn = new Mongo();
db = conn.getDB("db-name");  //选择数据库
db.auth("user-name","password");  //用户验证

var cursor = db.mr_result.find();

while(cursor.hasNext()) {
    r = cursor.next();
    print(r["_id"] + "\t" + r["value"]);
}

$ mongo test02.js

a       1
code    1
collection      1
consider        1
contains        1
documents       1
error   1
follow  1
following       3
found   1
get     1
i       2
in      1
link    1
map-reduce      1
of      1
on      1
operations      1
orders  1
prototype       1
that    1
the     4
this    1
when    1

function BaseOperation() {

    /*
    连接数据库，返回连接对象
    */
    this.getDB = function() {
        conn = new Mongo();
        db = conn.getDB("db-name");
        db.auth("user-name","password");
        return db;
    }
}

load("lib/base_operation.js");
BO = new BaseOperation();
db = BO.getDB();

var cursor = db.mr_result.find();

while(cursor.hasNext()) {
    r = cursor.next();
    print(r["_id"] + "\t" + r["value"]);
}