查询MongoDB Map Reduce函数

Question

我已经流式传输并将大约25万条推文保存到MongoDB中,在这里,我正在检索它,正如您所看到的,基于推文中出现的单词或关键字.

Mongo mongo = new Mongo("localhost", 27017);
DB db = mongo.getDB("TwitterData");
DBCollection collection = db.getCollection("publicTweets");
BasicDBObject fields = new BasicDBObject().append("tweet", 1).append("_id", 0);
BasicDBObject query = new BasicDBObject("tweet", new BasicDBObject("$regex", "autobiography"));
DBCursor cur=collection.find(query,fields);

我想要做的是使用Map-Reduce并根据关键字对其进行分类并将其传递给reduce函数来计算每个类别下的推文数量,有点像你在这里看到的.在这个例子中,他正在计算页数,因为它是一个简单的数字.我想做的事情如下:

"if (this.tweet.contains("kword1")) "+
"category = 'kword1 tweets'; " + 
"else if (this.tweet.contains("kword2")) " + 
"category = 'kword2 tweets'; 

然后使用reduce函数来获取计数,就像在示例程序中一样.

我知道语法不正确,但这就是我想做的事情.有没有办法实现它？谢谢!

PS:哦,我用Java编写代码.因此,Java语法将受到高度赞赏.谢谢!

发布的代码输出如下:

{ "tweet" : "An autobiography is a book that reveals nothing bad about its writer except his memory."}
{ "tweet" : "I refuse to read anything that's not real the only thing I've read since biff books is Jordan's autobiography #lol"}
{ "tweet" : "well we've had the 2012 publication of Ashley's Good Books, I predict 2013 will be seeing an autobiography ;)"}

当然,这是所有推文都带有"自传"一词.我想要的是在map函数中使用它,将其归类为"自传推文"(以及其他关键字),然后将其发送到reduce函数以计算所有内容并返回带有单词的推文数量它.

就像是:

{"_id" : "Autobiography Tweets" , "value" : { "publicTweets" : 3.0}}
{"_id" : "Biography Tweets" , "value" : { "publicTweets" : 15.0}}

Answer 1

您可能想尝试以下操作:

    String map = "function() { " +
                 "    var regex1 = new RegExp('autobiography', 'i'); " +
                 "    var regex2 = new RegExp('book', 'i'); " +
                 "    if (regex1.test(this.tweet) ) " +
                 "         emit('Autobiography Tweet', 1); " +
                 "    else if (regex2.test(this.tweet) ) " +
                 "         emit('Book Tweet', 1); " +
                 "    else " +
                 "       emit('Uncategorized Tweet', 1); " +
                 "}";

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

    MapReduceCommand cmd = new MapReduceCommand(collection, map, reduce,
             null, MapReduceCommand.OutputType.INLINE, null);
    MapReduceOutput out = collection.mapReduce(cmd);

    try {
        for (DBObject o : out.results()) {

            System.out.println(o.toString());

       }
    } catch (Exception e) {
        e.printStackTrace();
    }    

Answer 2

虽然你已经接受了Kay的答案,但这个可能会被忽略,我想建议一个替代解决方案.

MongoDB文档中有一篇关于如何在Mongo中执行全文搜索的文章.为了快速搜索基于文本的字段以查找单个单词,他们建议通过将文本字段拆分为单个单词的数组来准备文档,将这些数组与全文一起存储在文档中,并为此创建索引阵列.

之后,您可以非常快速地找到包含特定单词的所有文档,因为您的搜索查询可以1.使用索引而不必使用正则表达式(这可能非常昂贵).