The Elasticsearch Aggregations framework collects all the data selected by the search query and consists of many building blocks, which help in building complex summaries of the data. The basic structure of aggregation is shown here −
"aggregations" : {
"" : {
"" : {
}
[,"meta" : { [] } ]?
[,"aggregations" : { []+ } ]?
}
[,"" : { ... } ]*
}
There are different types of Elasticsearch Aggregations, each with its own purpose.
They are discussed in detail in this chapter.
Metrics Aggregations
These aggregations help in computing matrices from the field’s values of the aggregated documents and sometimes some values can be generated from scripts.
Numeric matrices are either single-valued like average aggregation or multi-valued like stats.
Avg Aggregation
This aggregation is used to get the average of any numeric field present in the aggregated documents. For example,
POST /schools/_search
{
"aggs":{
"avg_fees":{"avg":{"field":"fees"}}
}
}
On running the above code, we get the following result −
{
"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
}
}
}
Cardinality Aggregation
This aggregation gives the count of distinct values of a particular field.
POST /schools/_search?size=0
{
"aggs":{
"distinct_name_count":{"cardinality":{"field":"fees"}}
}
}
On running the above code, we get the following result −
{
"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
}
}
}
Note − The value of cardinality is 2 because there are two distinct values in fees.
Extended Stats Aggregation
This aggregation generates all the statistics about a specific numerical field in aggregated documents.
POST /schools/_search?size=0
{
"aggs" : {
"fees_stats" : { "extended_stats" : { "field" : "fees" } }
}
}
On running the above code, we get the following result −
{
"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
}
}
}
}
Max Aggregation
This aggregation finds the max value of a specific numeric field in aggregated documents.
POST /schools/_search?size=0
{
"aggs" : {
"max_fees" : { "max" : { "field" : "fees" } }
}
}
On running the above code, we get the following result −
{
"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 min value of a specific numeric field in aggregated documents.
POST /schools/_search?size=0
{
"aggs" : {
"min_fees" : { "min" : { "field" : "fees" } }
}
}
On running the above code, we get the following result −
{
"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 calculates the sum of a specific numeric field in aggregated documents.
POST /schools/_search?size=0
{
"aggs" : {
"total_fees" : { "sum" : { "field" : "fees" } }
}
}
On running the above code, we get the following result −
{
"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
}
}
}
There are some other metrics aggregations that are used in special cases like geo bounds aggregation and geo centroid aggregation for the purpose of geolocation.
Stats Aggregations
A multi-value metrics aggregation that computes stats over numeric values extracted from the aggregated documents.
POST /schools/_search?size=0
{
"aggs" : {
"grades_stats" : { "stats" : { "field" : "fees" } }
}
}
On running the above code, we get the following result −
{
"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
}
}
}
Aggregation Metadata
You can add some data about the aggregation at the time of request by using meta tag and can get that in response.
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 −
{
"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
}
}
}
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