Elasticsearch: The Definitive Guide

Chapter 27. Building Bar Charts

One of the exciting aspects of aggregations are how easily they are converted into charts and graphs. In this chapter, we are focusing on various analytics that we can wring out of our example dataset. We will also demonstrate the types of charts aggregations can power.

The histogram bucket is particularly useful. Histograms are essentially bar charts, and if you’ve ever built a report or analytics dashboard, you undoubtedly had a few bar charts in it. The histogram works by specifying an interval. If we were histogramming sale prices, you might specify an interval of 20,000. This would create a new bucket every $20,000. Documents are then sorted into buckets.

For our dashboard, we want to know how many cars sold in each price range. We would also like to know the total revenue generated by that price bracket. This is calculated by summing the price of each car sold in that interval.

To do this, we use a histogram and a nested sum metric:

GET /cars/transactions/_search?search_type=count
{
   "aggs":{
      "price":{
         "histogram":{ 
            "field": "price",
            "interval": 20000
         },
         "aggs":{
            "revenue": {
               "sum": { 
                 "field" : "price"
               }
             }
         }
      }
   }
}

The histogram bucket requires ...