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# Method name: avg(propertyName: string, projectedName: string)

# Method package: wixData

# Method menu location: wixData --> WixDataAggregate --> avg

# Method Link: https://dev.wix.com/docs/velo/apis/wix-data/wix-data-aggregate/avg.md

# Method Description:

Refines a `WixDataAggregate` to only contain the average value from each aggregation group.

The `avg()` function refines a `WixDataAggregate` to contain the average
 value from the specified property for each aggregated group or from the
 whole collection if no group is defined.

 When the aggregation is [run](#run), the returned `WixDataAggregateResult`
 object contains an item for each group with the following `key:value` pairs:

 + If a value was passed for the optional `projectedName`, the key is named
   using that value. Otherwise, the key is named using the following format:
   `"propertyNameAvg"`, where `propertyName` is the name of the specified property.
 + The value is the average of the values found in the specified property.


 Averages can only be calculated on properties of type Number.
 > **Note:** Aggregations can only be used on collections you have created. They cannot be
 used on [Wix App Collections](https://support.wix.com/en/article/cms-formerly-content-manager-working-with-wix-app-collections).



# Method Code Examples:

*** Note: do not assume any prop names or enum values other than the ones in the example.

## Add an avg aggregation

```javascript
let newAggregate = aggregate.avg("population");
```

## Add an avg aggregation with a projected name for the results

```javascript
let newAggregate = aggregate.max("population", "avgPopulation");
```

## Create an aggregation, add an avg aggregation, and run it

```javascript
import wixData from 'wix-data';

// ...

wixData.aggregate("PopulationData")
  .group("state", "year")
  .avg("population")
  .run()
  .then((results) => {
    let items = results.items;        // see below
    let numItems = results.length;    // 6
    let hasNext = results.hasNext();  // false
  })
  .catch((error) => {
    let errorMsg = error.message;
    let code = error.code;
  });

/* Given the sample data above, items is:
 * [
 *   {
 *     "_id": {"state": "NY", "year": 2000},
 *     "populationAvg": 4153500,
 *     "state": "NY",
 *     "year": 2000},
 *   {
 *     "_id": {"state": "FL", "year": 2000},
 *     "populationAvg": 278500,
 *     "state": "FL",
 *     "year": 2000
 *   },
 *   {
 *     "_id": {"state": "CA", "year": 2000},
 *     "populationAvg": 2240000,
 *     "state": "CA",
 *     "year": 2000
 *   },
 *   {
 *     "_id": {"state": "FL", "year": 2010},
 *     "populationAvg": 320500,
 *     "state": "FL",
 *     "year": 2010
 *   },
 *   {
 *     "_id": {"state": "CA", "year": 2010},
 *     "populationAvg": 2300500,
 *     "state": "CA",
 *     "year": 2010
 *   },
 *   {
 *     "_id": {"state": "NY", "year": 2010},
 *     "populationAvg": 4226500,
 *     "state": "NY",
 *     "year": 2010
 *   }
 * ]
 */
```

## Create an aggregation, add an avg aggregation with a projected name for the results, and run it

```javascript
import wixData from 'wix-data';

// ...

wixData.aggregate("PopulationData")
  .group("state", "year")
  .avg("population", "averagePopulation")
  .run()
  .then((results) => {
    let items = results.items;        // see below
    let numItems = results.length;    // 6
    let hasNext = results.hasNext();  // false
  })
  .catch((error) => {
    let errorMsg = error.message;
    let code = error.code;
  });

/* Given the sample data above, items is:
 * [
 *   {
 *     "_id": {"state": "NY", "year": 2000},
 *     "averagePopulation": 4153500,
 *     "state": "NY",
 *     "year": 2000},
 *   {
 *     "_id": {"state": "FL", "year": 2000},
 *     "averagePopulation": 278500,
 *     "state": "FL",
 *     "year": 2000
 *   },
 *   {
 *     "_id": {"state": "CA", "year": 2000},
 *     "averagePopulation": 2240000,
 *     "state": "CA",
 *     "year": 2000
 *   },
 *   {
 *     "_id": {"state": "FL", "year": 2010},
 *     "averagePopulation": 320500,
 *     "state": "FL",
 *     "year": 2010
 *   },
 *   {
 *     "_id": {"state": "CA", "year": 2010},
 *     "averagePopulation": 2300500,
 *     "state": "CA",
 *     "year": 2010
 *   },
 *   {
 *     "_id": {"state": "NY", "year": 2010},
 *     "averagePopulation": 4226500,
 *     "state": "NY",
 *     "year": 2010
 *   }
 * ]
 */
```

---