3. Nested Aggregation

A nested aggregation permits you to assemble a field with nested reports, a field that has numerous sub-fields.A unique single bucket aggregation that empowers accumulating nested archives. For instance, let’s state we have a list of products, and every item holds the list of resellers, each having its own cost for the item.  Resellers is an array that holds nested documents. The mapping could resemble:

PUT /products
{
  "mappings": {
    "properties": {
      "resellers": { 
        "type": "nested",
        "properties": {
          "reseller": { "type": "text" },
          "price": { "type": "double" }
        }
      }
    }
  }
}
The following request adds a product with two resellers:
PUT /products/_doc/0
{
  "name": "LED TV", 
  "resellers": [
    {
      "reseller": "companyA",
      "price": 350
    },
    {
      "reseller": "companyB",
      "price": 500
    }
  ]
}

The following request returns the minimum price a product can be purchased for:

GET /products/_search
{
  "query": {
    "match": { "name": "led tv" }
  },
  "aggs": {
    "resellers": {
      "nested": {
        "path": "resellers"
      },
      "aggs": {
        "min_price": { "min": { "field": "resellers.price" } }
      }
    }
  }
}
Output
{
  ...
  "aggregations": {
    "resellers": {
      "doc_count": 2,
      "min_price": {
        "value": 350
      }
    }
  }
 }

4. Cardinality Aggregation

This aggregation gives the tally of distinct values in a specific field. It helps to find a unique value for a field. 

POST /schools/_search?size=0

{
   "aggs":{
      "distinct_name_count":{"cardinality":{"field":"fees"}}
   }
}
On running the above code, we get the following result,
Output
{
   "took" : 2,
   "timed_out" : false,
   "_shards" : {
      "total" : 1,
      "successful" : 1,
      "skipped" : 0,
      "failed" : 0
   },
   "hits" : {
      "total" : {
         "value" : 2,
         "relation" : "eq"
      },
      "max_score" : null,
      "hits" : [ ]
   },
   "aggregations" : {
      "distinct_name_count" : {
         "value" : 2
      }
   }
}
The value of cardinality is 2 because there are two distinct values in fees.

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5. Extended Stats Aggregation

This aggregation produces all the statistics about a particular mathematical field in collected documents. 

POST /schools/_search?size=0

{
   "aggs" : {
      "fees_stats" : { "extended_stats" : { "field" : "fees" } }
   }
}
On running the above code, we get the following result,
Output
{
   "took" : 8,
   "timed_out" : false,
   "_shards" : {
      "total" : 1,
      "successful" : 1,
      "skipped" : 0,
      "failed" : 0
   },
   "hits" : {
      "total" : {
         "value" : 2,
         "relation" : "eq"
      },
      "max_score" : null,
      "hits" : [ ]
   },
   "aggregations" : {
      "fees_stats" : {
         "count" : 2,
         "min" : 2200.0,
         "max" : 3500.0,
         "avg" : 2850.0,
         "sum" : 5700.0,
         "sum_of_squares" : 1.709E7,
         "variance" : 422500.0,
         "std_deviation" : 650.0,
         "std_deviation_bounds" : {
            "upper" : 4150.0,
            "lower" : 1550.0
         }
      }
   }
}

6. Stats Aggregation

A multi-value metrics aggregation that figures statistics over numeric values removed from the aggregated reports. It is a multi-value numeric matrix aggregation that helps to create sum, avg, max, min, and count in a single shot. The query structure is the same as the other aggregation

POST /schools/_search?size=0

{
   "aggs" : {
      "grades_stats" : { "stats" : { "field" : "fees" } }
   }
}
On running the above code, we get the following result,
Output
{
   "took" : 2,
   "timed_out" : false,
   "_shards" : {
      "total" : 1,
      "successful" : 1,
      "skipped" : 0,
      "failed" : 0
   },
   "hits" : {
      "total" : {
         "value" : 2,
         "relation" : "eq"
      },
      "max_score" : null,
      "hits" : [ ]
   },
   "aggregations" : {
      "grades_stats" : {
         "count" : 2,
         "min" : 2200.0,
         "max" : 3500.0,
         "avg" : 2850.0,
         "sum" : 5700.0
      }
   }
}

Avg Aggregation

This collection is utilized to get the avg of any numeric field present in the collected records. 

POST /schools/_search

{
   "aggs":{
      "avg_fees":{"avg":{"field":"fees"}}
   }
}
On running the above code, we get the following result −
Output
{
   "took" : 41,
   "timed_out" : false,
   "_shards" : {
      "total" : 1,
      "successful" : 1,
      "skipped" : 0,
      "failed" : 0
   },
   "hits" : {
      "total" : {
         "value" : 2,
         "relation" : "eq"
      },
      "max_score" : 1.0,
      "hits" : [
         {
            "_index" : "schools",
            "_type" : "school",
            "_id" : "5",
            "_score" : 1.0,
            "_source" : {
               "name" : "Central School",
               "description" : "CBSE Affiliation",
               "street" : "Nagan",
               "city" : "paprola",
               "state" : "HP",
               "zip" : "176115",
               "location" : [
                  31.8955385,
                  76.8380405
               ],
            "fees" : 2200,
            "tags" : [
               "Senior Secondary",
               "beautiful campus"
            ],
            "rating" : "3.3"
         }
      },
      {
         "_index" : "schools",
         "_type" : "school",
         "_id" : "4",
         "_score" : 1.0,
         "_source" : {
            "name" : "City Best School",
            "description" : "ICSE",
            "street" : "West End",
            "city" : "Meerut",
            "state" : "UP",
            "zip" : "250002",
            "location" : [
               28.9926174,
               77.692485
            ],
            "fees" : 3500,
            "tags" : [
               "fully computerized"
            ],
            "rating" : "4.5"
         }
      }
   ]
 },
   "aggregations" : {
      "avg_fees" : {
         "value" : 2850.0
      }
   }
}

Max Aggregation

This aggregation finds the maximum value of a particular numeric field in collected archives. 

POST /schools/_search?size=0

{
   "aggs" : {
   "max_fees" : { "max" : { "field" : "fees" } }
   }
}
On running the above code, we get the following result −
Output
{
   "took" : 16,
   "timed_out" : false,
   "_shards" : {
      "total" : 1,
      "successful" : 1,
      "skipped" : 0,
      "failed" : 0
   },
  "hits" : {
      "total" : {
         "value" : 2,
         "relation" : "eq"
      },
      "max_score" : null,
      "hits" : [ ]
   },
   "aggregations" : {
      "max_fees" : {
         "value" : 3500.0
      }
   }
}

Min Aggregation

This aggregation finds the maximum value of a particular numeric field in collected archives. 

POST /schools/_search?size=0

{
   "aggs" : {
      "min_fees" : { "min" : { "field" : "fees" } }
   }
}
On running the above code, we get the following result −
Output
{
   "took" : 2,
   "timed_out" : false,
   "_shards" : {
      "total" : 1,
      "successful" : 1,
      "skipped" : 0,
      "failed" : 0
   },
   "hits" : {
      "total" : {
         "value" : 2,
         "relation" : "eq"
      },
      "max_score" : null,
      "hits" : [ ]
   },
  "aggregations" : {
      "min_fees" : {
         "value" : 2200.0
      }
   }
}

Sum Aggregation

This aggregation finds the maximum value of a particular numeric field in collected archives.

POST /schools/_search?size=0

{
   "aggs" : {
      "total_fees" : { "sum" : { "field" : "fees" } }
   }
}
On running the above code, we get the following result −
Output
{
   "took" : 8,
   "timed_out" : false,
   "_shards" : {
      "total" : 1,
      "successful" : 1,
      "skipped" : 0,
      "failed" : 0
   },
   "hits" : {
      "total" : {
         "value" : 2,
         "relation" : "eq"
      },
      "max_score" : null,
      "hits" : [ ]
   },
   "aggregations" : {
      "total_fees" : {
         "value" : 5700.0
      }
   }
}

7. Aggregation Metadata

You can add some information about the aggregation at the hour of solicitation by utilizing meta tag and can get that accordingly.

POST /schools/_search?size=0

{
   "aggs" : {
      "min_fees" : { "avg" : { "field" : "fees" } ,
         "meta" :{
            "dsc" :"Lowest Fees This Year"
         }
      }
   }
}
On running the above code, we get the following result −
Output
{
   "took" : 0,
   "timed_out" : false,
   "_shards" : {
      "total" : 1,
      "successful" : 1,
      "skipped" : 0,
      "failed" : 0
   },
   "hits" : {
      "total" : {
         "value" : 2,
         "relation" : "eq"
      },
      "max_score" : null,
      "hits" : [ ]
   },
   "aggregations" : {
      "min_fees" : {
         "meta" : {
            "dsc" : "Lowest Fees This Year"
         },
         "value" : 2850.0
      }
   }
}

Conclusion

The different types of aggregations have their own purpose and functions. We have discussed it in detail about it using the coding examples. There exists metrics aggregations that are used in particular cases such as geo bounds aggregation and geo centroid aggregation to get the understanding of geo location. You could understand the concept of aggregation through the examples provided.

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