AQL aggregation functions syntax

Question

What exactly is the syntax for aggregation functions like sum()?

For example, take the following structure:

let json = {
    "ages": {
    "age": [
    "20",
    "30",
    "40"
    ]
    }
}

and that

for age in json.ages.age return age

returns

 ["20", "30", "40"]

All of the following snippets return "[1542] invalid argument type used in call to function 'SUM()'" in Arango 2.0.4:

// LR
let ages = (for age in json.ages.age return age)
return sum(ages)

// LR
let ages = (
    for age in json.ages.age  
    return age
)
return sum((for age in json.ages.age return age))

// R
return sum((for age in json.ages.age return age))

What is the correct syntax?

The syntax page (http://www.arangodb.org/manuals/current/Aql.html#AqlFunctionsList) does not appear to have any related examples.

The closest thing I could find to a syntax example is this: https://www.arangodb.org/foxx

controller.get("/revenue/:year", function (req, res) {
  var query = "RETURN SUM((FOR bill IN billcollection FILTER bill.year == @year     RETURN     bill.amount))"; 
  var stmt = db._createStatement({ "query": query});
  stmt.bind("year",parseInt(req.params("year"),10));
  var c = stmt.execute();
  res.json(c);
});

but it seems to have the syntax above that is failing for me.

Is there a more detailed syntax reference anywhere?

Answer 1

Your approach is correct, however you missed a tiny spot in the docs. ;)

In the docs for SUM() it says:

SUM(list) : returns the sum of the values in list. This requires the elements in list to be numbers. null values are ignored.

(Docs reference: https://www.arangodb.org/manuals/current/Aql.html#AqlFunctionsList)

Note the "This requires the elements in list to be numbers"

So, your JSON-example should have numbers in the list, instead of strings.

let json = {
    "ages": {
    "age": [
        20,
        30,
        40
    ]
    }
}

let ages = (for age in json.ages.age return age)
return sum(ages)

Copying and running the above snippet into your AQL editor should result in the desired:

[
  90
]

You can of course also leave your json intact and type-cast the strings into numbers by changing the AQL query accordingly:

let json = {
    "ages": {
    "age": [
        "20",
        "30",
        "40"
    ]
    }
}

let ages = (for age in json.ages.age return TO_NUMBER(age))
return sum(ages)