In CouchDB, how do you find the most common value?

I am trying to classify aggregation levels by finding the most common value of a specific field in documents that are flattened to a given level.

I have documents like this:

{ year: 2012,
  month: 01,
  category: blue
},

{ year: 2012,
  month: 01,
  category: blue
},

{ year: 2012,
  month: 01,
  category: blue
},

{ year: 2012,
  month: 01,
  category: green
}

      

The map function basically emits these documents with keys like [year, month]

(although I could include a category if needed). I shrink it to shrink it down to the most common category.

In the case of my above examples, group = false, level_1 and level_2 should all boil down to "blue".

I was thinking about trying to change the key to [year, month, category]

with the hope that I can count the values โ€‹โ€‹of the categories when I moved the aggregation. But it doesn't work.

How do I find the most common meaning for a category? I feel like the answer is simple, but I just don't connect the dots.

Thank.

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1 answer


It's simple, but not concise as I worked.



{
   "views": {
       "most_category": {
           "map": "function(doc){
             if (doc.category && doc.year && doc.month) {
                var hash = {};
                hash[doc.category] = 1;
                emit([doc.year, doc.month], hash);
             }
           }",
           "reduce": "function(keys, values, rereduce) {
              var agg = values[0];
              for (var i = 1; i < values.length; ++i) {
                for (var category in values[i]) {
                  if (agg[category]) {
                    agg[category] += values[i][category];
                  } else {
                    agg[category] = values[i][category];
                  }
                }
              }
              var most_category = null;
              var most_count = 0;
              for (var category in agg) {
                if (most_count<agg[category]) {
                  most_category = category;
                  most_count = agg[category];
                }
              }
              var hash = {};
              hash[most_category] = most_count;
              return hash;
           }"
       }
   }
}

      

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