How to Find the Max with Aggregations in Elasticsearch using NodeJS

Written by Data Pilot
April 07, 2019
  • Elasticsearch
  • NodeJS
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Introduction

Aggregation is a very powerful functionality in Elasticsearch. In this article we’ll be showing you how to use aggregations with NodeJS to find the maximum value for a field in a dataset. Aggregations can do many things like histograms, sums, or averages but finding the max and min are a good way to get your feet wet with aggregations. We’ll show you how step-by-step. But if you’d just rather see the example code, click here to jump to Just the Code.

Prerequisites

Before we show you how to find the maximum value using Elasticsearch, it’s important to make sure a few prerequisites are in place. There are only a few of system requirements for this task: NodeJS needs to be installed Elasticsearch also needs to be installed and running. In our example, we have Elasticsearch installed locally using the default port of 9200. If your Elasticsearch installation is running on a different server, you’ll need to modify your javascript syntax accordingly. The elasticsearch npm module installed. * A simple npm install elasticsearch should work in most cases.

Use the max Aggregation

We love to show by example. In this example we use an index representing a small grocery store called `store`. The `store` index contains the type `products` which lists all the stores products. To keep it simple our dataset only has a small number of products with just a few fields including the id, price, quantity, and department.

Here is our dataset:

idnamepricequantitydepartment
1Multi-Grain Cereal4.994Packaged Foods
21lb Ground Beef3.9929Meat and Seafood
3Dozen Apples2.4912Produce
4Chocolate Bar1.292Packaged FoodsCheckout
51 Gallon Milk3.2916Dairy
60.5lb Jumbo Shrimp5.2912Meat and Seafood
7Wheat Bread1.295Bakery
8Pepperoni Pizza2.995Frozen
912 Pack Cola5.296Packaged Foods
10Lime Juice0.9920Produce
1112 Pack Cherry Cola5.595Packaged Foods
121 Gallon Soy Milk3.3910Dairy
131 Gallon Vanilla Soy Milk3.499Dairy
141 Gallon Orange Juice3.294Juice

And here is the json we used to make the mapping:

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{
    "mappings": {`
        "products": {
            "properties" : {`
                "name": { "type": "text"},
                "price": { "type": "double"},
                "quantity": { "type": "integer"},
                "department": { "type": "keyword"}
            }
        }
    }
}

To demonstrate how to find the maximum, we will take our store index and find the product with the highest price. If you look at our data, the highest price is this product ($5.59):

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11| 12 Pack Cherry Cola | 5.59 | 5 | Packaged Foods

Let’s look at the code of how we’d determine the highest price of a product and then we’ll explain it:

File index.js:

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var elasticsearch = require("elasticsearch");

var client = new elasticsearch.Client({
  hosts: ["http://localhost:9200"]
});

/* Aggregate Max */
client.search({
  index: 'store',
  type: 'products',
  body: {
      aggs: {
        max_price: {
          max:
            {
              field: "price"
            }
        }
      }
  }
}).then(function(resp) {
  console.log("Successful query! Here is the response:", resp);
}, function(err) {
  console.trace(err.message);
});

There’s a few steps to dissect so let’s dive in step-by-step: First we required the elasticsearch library because it gives us the library of functions that make it easy to access Elasticsearch. Next we created a variable var client which creates and stores our connection to Elasticsearch. From this point on we’ll use this client to do all our interactions with Elasticsearch. We then use the search function on client to create a query with an aggregator. Of course we specify the index and type to perform the search on. The important part comes in the body where we define the aggregator by using the aggs keyword. We gave our aggregator a name max_price that can be anything but choose something that makes sense. We specify the type of aggregator as max. * Lastly we specify what field the aggregator should evaluate, price.

Now let’s see the result:

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$ node index.js
Successful query! Here is the response: { took: 76,
  timed_out: false,
  _shards: { total: 5, successful: 5, skipped: 0, failed: 0 },
  hits:
   { total: 13,
     max_score: 1,
     hits:
      [ [Object],
        [Object],
        [Object],
        [Object],
        [Object],
        [Object],
        [Object],
        [Object],
        [Object],
        [Object] ] },
  aggregations: { max_price: { value: 5.99 } } }

As you can see our max_price returned a value of $5.59 just as we expected.

This is just as easily done for finding the minimum by replacing the max with min.

Conclusion

In this tutorial we demonstrated how to use Elasticsearch aggregations to get the minimum or maximum value for a field in a given dataset. Remember that these are the most basic of aggregators and the to explore the myriad of other options and combinations available. Consult the documentation for more information on aggregators and specific syntax. Their documentation is full of great examples.

We hope you found tutorial helpful and you can apply it to your specific application. If you have questions or this didn’t work for you please reach out to us so we can help. Thank you.

Just the Code

If you’re already comfortable with NodeJS and aggregations here’s all the code we used to demonstrate how to find the max for a field in our dataset.

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var elasticsearch = require("elasticsearch");

var client = new elasticsearch.Client({
  hosts: ["http://localhost:9200"]
});

/* Aggregate Max */
client.search({
  index: 'store',
  type: 'products',
  body: {
      aggs: {
        max_price: {
          max:
            {
              field: "price"
            }
        }
      }
  }
}).then(function(resp) {
  console.log("Successful query! Here is the response:", resp);
}, function(err) {
  console.trace(err.message);
});
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