index.md

Elastic Stack Lab 14

In this lab we are going to use aggregates with our indices.

Let's start by running a query on the ratings index and requesting ratings for all movies.

curl -XGET '127.0.0.1:9200/ratings/rating/_search?size=0&pretty' -d '
{
    "aggs": {
        "ratings": {
            "terms": {
                "field": "rating"
            }
        }
    }
}'

In the above command we specified size=0 so that we avoid having Elasticsearch return all documents that match, and only returning the results of our ratings query.

You can now see the number of documents that have specific ratings. Not surprising 4.0 is the largest rating used.

Now let's try a query that's a bit more complicated. We are going to pull back only 5.0 rated movies.

curl -XGET '127.0.0.1:9200/ratings/rating/_search?size=0&pretty' -d '
{
    "query": {
        "match": { "rating": 5.0 }
    },
    "aggs": {
        "ratings": {
            "terms": { "field": "rating" }
        }
    }
}'
             

A good practice for using aggregate is to start with a query block to narrow down the results and then use an aggregation to add up the remaining documents.

Now let's get an aggregation for the average rating of "Star Wars Episode IV"

curl -XGET '127.0.0.1:9200/ratings/rating/_search?size=0&pretty' -d '
{
    "query": {
        "match_phrase" : {"title" : "Star Wars Episode IV" }
        }
        ,
        "aggs": {
                "avg_rating": {
                     "avg": {"field" : "rating"}
        }
    }
}'

Histograms

Histograms are a great way to retrieve data that can easily be used for visual graphs.

Let's start by creating a query which will show us ratings grouped by whole number.

curl -XGET '127.0.0.1:9200/ratings/rating/_search?size=0&pretty' -d '
{
    "aggs": {
        "whole_ratings": {
            "histogram": {
                "field": "rating",
                 "interval": 1.0
            }
        }
    }
}'

The output of this query should show you ratings grouped by whole number.

Now let's bucket up all the movies by release year.

curl -XGET '127.0.0.1:9200/movies/movie/_search?size=0&pretty' -d '
{
    "aggs": {
        "release": {
            "histogram": {
               "field": "year",
               "interval": 10
            }
        }
    }
}'

This query will return results of how many movies were released each decade.

Lab Complete