How do you sort results of a _View_ by value in the in Couchbase?

问题

So from what I understand in Couchbase is that one can sort keys* by using

descending=true

but in my case I want to sort by values instead. Consider the Twitter data in json format, my question is What it the most popular user mentioned?

Each tweet has the structure of:

{
    "text": "",
    "entities" : {
        "hashtags" : [ ... ],
        "user_mentions" : [ ...],
        "urls" : [ ... ]
}

So having used MongoDB before I reused the Map function and modified it slightly to be usable in Couchbase as follows:

function (doc, meta) {
  if (!doc.entities) { return; }

  doc.entities.user_mentions.forEach(
    function(mention) {
      if (mention.screen_name !== undefined) {
        emit(mention.screen_name, null);
      }
    }
  )
}

And then I used the reduce function _count to count all the screen_name occurrences. Now my problem is How do I sort by the count values, rather than the key?

Thanks

回答1:

The short answer is you cannot sort by value the result of you view. You can only sort by key.

Some work around will be to either:

analyze the data before inserting them into Couchbase and create a counter for the values you are interested by (mentions in your case)
use the view you have to sort on the application size if the size of the view is acceptable for a client side sort.

The following JS code calls a view, sorts the result, and prints the 10 hottest subjects (hashtags):

var http =  require('http');

var options = {
    host: '127.0.0.1',
    port: 8092,
    path: '/social/_design/dev_tags/_view/tags?full_set=true&connection_timeout=60000&group=true',
    method: 'GET'
}

http.request(
    options, 
    function(res) {
        var buf = new Buffer(0);
        res.on('data', function(data) {
            buf += data;
        });
        res.on('end', function() {
            var tweets = JSON.parse(buf);
            var rows = tweets.rows;
            rows.sort( function (a,b){ return b.value - a.value } 
            );


            for ( var i = 0;  i < 10; i++ ) {
                console.log( rows[i] );
            }
        });
    }
    ).end();

In the same time I am looking at other options to achieve this

回答2:

I solved this by using a compound key.

function (doc, meta) {
  emit([doc.constraint,doc.yoursortvalue]);
}

url elements:

&startkey=["jim",5]&endkey=["jim",10]&descending=true

来源：https://stackoverflow.com/questions/13292609/how-do-you-sort-results-of-a-view-by-value-in-the-in-couchbase

标签

MapReduce

couchdb

couchbase

nosql-aggregation