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Aggregate Values Over a Dataset
In this section, we learn how to get TypeDB to calculate the count, sum, max, mean, and median values of a specific set of data in the knowledge graph.
To perform aggregation in TypeDB, we first write a match clause to describe the set of data, then follow that by get to retrieve a distinct set of answers based on the specified variables, and lastly an aggregate function to perform on the variable of interest.
To try the following examples with one of the TypeDB clients, follows these Clients Guide.
Count
We use the count function to get the number of the specified matched variable.
[tab:TypeQL]
```typeql
match
$sce isa studentship, has score $sco;
$sco > 7.0;
get $sco; count;
```
[tab:end]
[tab:Java]
```java
TypeQLMatch.Unfiltered.Aggregate query = TypeQL.match(
var("sce").isa("studentship").has("score", var("sco")),
var("sco").gt(7.0)
).get("sce").count();
```
[tab:end]
[Note]
When more than one variable follows the `get` keyword, the `count` function is applied on the unique set of the retrieved variables. This is also the case, when no variable follows `get`, which actually means all matched variables are included.
Sum
We use the sum function to get the sum of the specified long or double matched variable.
[tab:TypeQL]
```typeql
match
$org isa organisation, has name $orn;
$orn "Medicely";
($org) isa employment, has salary $sal;
get $sal; sum $sal;
```
[tab:end]
[tab:Java]
```java
TypeQLMatch.Unfiltered.Aggregate query = TypeQL.match(
var("org").isa("organisation").has("name", var("orn")),
var("orn").eq("Medicely"),
var().rel("org").isa("employment").has("salary", var("sal"))
).get("sal").sum("sal");
```
[tab:end]
Maximum
We use the max function to get the maximum value among the specified long or double matched variable.
[tab:TypeQL]
```typeql
match
$sch isa school, has ranking $ran;
get $ran; max $ran;
```
[tab:end]
[tab:Java]
```java
TypeQLMatch.Unfiltered.Aggregate query = TypeQL.match(
var("sch").isa("school").has("ranking", var("ran"))
).get("ran").max("ran");
```
[tab:end]
Minimum
We use the min function to get the minimum value among the specified long or double matched variable.
[tab:TypeQL]
```typeql
match
($per) isa marriage;
($per) isa employment, has salary $sal;
get $sal; min $sal;
```
[tab:end]
[tab:Java]
```java
TypeQLMatch.Unfiltered.Aggregate query = TypeQL.match(
var().rel(var("per")).isa("marriage"),
var().rel(var("per")).isa("employment").has("salary", var("sal"))
).get("sal").min("sal");
```
[tab:end]
Mean
We use the mean function to get the average value of the specified long or double matched variable.
[tab:TypeQL]
```typeql
match
$emp isa employment, has salary $sal;
get $sal; mean $sal;
```
[tab:end]
[tab:Java]
```java
TypeQLMatch.Unfiltered.Aggregate query = TypeQL.match(
var("emp").isa("employment").has("salary", var("sal"))
).get("sal").mean("sal");
```
[tab:end]
We use the median function to get the median value among the specified long or double matched variable.
[tab:TypeQL]
```typeql
match
$org isa organisation, has name $orn;
$orn = "Facelook";
(employer: $org, employee: $per) isa employment;
($per) isa studentship, has score $sco;
get $sco; median $sco;
```
[tab:end]
[tab:Java]
```java
TypeQLMatch.Unfiltered.Aggregate query = TypeQL.match(
var("org").isa("organisation").has("name", var("orn")),
var("orn").eq("Facelook"),
var().rel("employer", var("org")).rel("employee", var("per")).isa("employment"),
var().rel(var("per")).isa("studentship").has("score", var("sco"))
).get("sco").median("sco");
```
[tab:end]
Grouping Answers
We use the group function, optionally followed by another aggregate function, to group the answers by the specified matched variable.
[tab:TypeQL]
```typeql
match
$per isa person;
$scc isa school-course, has title $title;
(student: $per, course: $scc) isa studentship;
get $scc, $title; group $title;
```
[tab:end]
[tab:Java]
```java
TypeQLMatch.Unfiltered.Group query = TypeQL.match(
var("per").isa("person"),
var("scc").isa("school-course").has("title", var("title")),
var().rel("student", var("per")).rel("course", var("scc")).isa("studentship")
).get("scc", "title").group("title");
```
[tab:end]
This query returns all instances of person grouped by the title of their school-course.
[tab:TypeQL]
```typeql
match
$per isa person;
$scc isa school-course, has title $title;
(student: $per, course: $scc) isa studentship;
get $scc, $title; group $title; count;
```
[tab:end]
[tab:Java]
```java
TypeQLMatch.Unfiltered.Group.Aggregate query = TypeQL.match(
var("per").isa("person"),
var("scc").isa("school-course").has("title", var("title")),
var().rel("student", var("per")).rel("course", var("scc")).isa("studentship")
).get("scc", "title").group("title").count();
```
[tab:end]
This query returns the total count of persons grouped by the title of their school-course.
Clients Guide
[Note]
**For those developing with Client [Java](../client-api/java)**: Executing a `match aggregate` query, is as simple as calling the [`query().match()`](../client-api/java) method on a transaction and passing the query object to it.
[Note]
**For those developing with Client [Node.js](../client-api/nodejs)**: Executing a `match aggregate` query, is as simple as passing the TypeQL(string) query to the `query().matchAggregate()` function available on the [`transaction`](../client-api/nodejs#transaction) object.
[Note]
**For those developing with Client [Python](../client-api/python)**: Executing a `match aggregate` query, is as simple as passing the TypeQL(string) query to the `query().match_aggregate()` method available on the [`transaction`](../client-api/python#transaction) object.
Summary
We use an aggregate query to calculate a certain variable as defined in the precedingmatch clause that describes a set of data in the knowledge graph.
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