---
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title: sumBy
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content_type: documentation
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release: "2.3"
latest: false
---
---
product: DataWeave
version: 2.3
---

# sumBy

> For the full documentation index, see: https://docs.mulesoft.com/llms.txt

## sumBy(Array<T>, (T) -> Number): Number

Returns the sum of the values of the elements in an array.

### Parameters

<table><colgroup><col> <col></colgroup><thead><tr><th>Name</th><th>Description</th></tr></thead><tbody><tr><td><p><code>array</code></p></td><td><p>The input array.</p></td></tr><tr><td><p><code>numberSelector</code></p></td><td><p>A DataWeave selector that selects the values of the numbers in the input array.</p></td></tr></tbody></table>

### Example

This example calculates the sum of the values of elements some arrays. Notice that both of the
`sumBy` function calls produce the same result.

#### Source

```DataWeave
 %dw 2.0
 import * from dw::core::Arrays
 output application/json
 ---
{
  "sumBy" : [
    [ { a: 1 }, { a: 2 }, { a: 3 } ] sumBy $.a,
    sumBy([ { a: 1 }, { a: 2 }, { a: 3 } ], (item) -> item.a)
  ]
}
```

#### Output

```json
{ "sumBy": [6, 6] }
```