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# ArrayGroupBy

Returns a struct of keys returned from the predicate function and values of arrays of matching rows.

```
 values = [ 1, 2, 3, 4 ];
 values.groupBy( ( value ) => value % 2 ? "odd" : "even" );
 // { odd: [ 1, 3 ], even: [ 2, 4 ] }
 
```

## Method Signature

```
ArrayGroupBy(array=[array], callback=[function])
```

### Arguments

| Argument   | Type       | Required | Description                                                                                                                                                                                      | Default |
| ---------- | ---------- | -------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------- |
| `array`    | `array`    | `true`   | The array to group.                                                                                                                                                                              |         |
| `callback` | `function` | `true`   | The function to invoke for each item. The function will be passed 3 arguments: the value, the index, the array. You can alternatively pass a Java Predicate which will only receive the 1st arg. |         |

## Examples

### Group array elements by a computed key

Returns a struct where each key is a value returned by the callback and each value is an array of matching elements.

```java
numbers = [ 1, 2, 3, 4, 5, 6 ];
groups = numbers.groupBy( ( n ) => n % 2 == 0 ? "even" : "odd" );
writeOutput( groups.keyList() );

```

Result: odd,even

### Group objects by a property

```java
users = [
    { name: "Alice", role: "admin" },
    { name: "Bob", role: "user" },
    { name: "Carol", role: "admin" }
];
byRole = users.groupBy( ( u ) => u.role );
writeOutput( byRole.admin.len() );

```

Result: 2

### Access a specific group

```java
numbers = [ 1, 2, 3, 4 ];
groups = numbers.groupBy( ( n ) => n % 2 == 0 ? "even" : "odd" );
writeOutput( groups.even.toString() );

```

Result: \[2, 4]

## Related

* [ArrayAppend](/boxlang-language/reference/built-in-functions/array/arrayappend.md)
* [ArrayAvg](/boxlang-language/reference/built-in-functions/array/arrayavg.md)
* [ArrayChunk](/boxlang-language/reference/built-in-functions/array/arraychunk.md)
* [ArrayClear](/boxlang-language/reference/built-in-functions/array/arrayclear.md)
* [ArrayContains](/boxlang-language/reference/built-in-functions/array/arraycontains.md)
* [ArrayContainsNoCase](/boxlang-language/reference/built-in-functions/array/arraycontainsnocase.md)
* [ArrayDelete](/boxlang-language/reference/built-in-functions/array/arraydelete.md)
* [ArrayDeleteAt](/boxlang-language/reference/built-in-functions/array/arraydeleteat.md)
* [ArrayDeleteNoCase](/boxlang-language/reference/built-in-functions/array/arraydeletenocase.md)
* [ArrayEach](/boxlang-language/reference/built-in-functions/array/arrayeach.md)
* [ArrayEvery](/boxlang-language/reference/built-in-functions/array/arrayevery.md)
* [ArrayFilter](/boxlang-language/reference/built-in-functions/array/arrayfilter.md)
* [ArrayFind](/boxlang-language/reference/built-in-functions/array/arrayfind.md)
* [ArrayFindAll](/boxlang-language/reference/built-in-functions/array/arrayfindall.md)
* [ArrayFindAllNoCase](/boxlang-language/reference/built-in-functions/array/arrayfindallnocase.md)
* [ArrayFindFirst](/boxlang-language/reference/built-in-functions/array/arrayfindfirst.md)
* [ArrayFindNoCase](/boxlang-language/reference/built-in-functions/array/arrayfindnocase.md)
* [ArrayFirst](/boxlang-language/reference/built-in-functions/array/arrayfirst.md)
* [ArrayFlatMap](/boxlang-language/reference/built-in-functions/array/arrayflatmap.md)
* [ArrayFlatten](/boxlang-language/reference/built-in-functions/array/arrayflatten.md)
* [ArrayGetMetadata](/boxlang-language/reference/built-in-functions/array/arraygetmetadata.md)
* [ArrayIndexExists](/boxlang-language/reference/built-in-functions/array/arrayindexexists.md)
* [ArrayInsertAt](/boxlang-language/reference/built-in-functions/array/arrayinsertat.md)
* [ArrayIsDefined](/boxlang-language/reference/built-in-functions/array/arrayisdefined.md)
* [ArrayLast](/boxlang-language/reference/built-in-functions/array/arraylast.md)
* [ArrayMap](/boxlang-language/reference/built-in-functions/array/arraymap.md)
* [ArrayMax](/boxlang-language/reference/built-in-functions/array/arraymax.md)
* [ArrayMedian](/boxlang-language/reference/built-in-functions/array/arraymedian.md)
* [ArrayMerge](/boxlang-language/reference/built-in-functions/array/arraymerge.md)
* [ArrayMid](/boxlang-language/reference/built-in-functions/array/arraymid.md)
* [ArrayMin](/boxlang-language/reference/built-in-functions/array/arraymin.md)
* [ArrayNew](/boxlang-language/reference/built-in-functions/array/arraynew.md)
* [ArrayNone](/boxlang-language/reference/built-in-functions/array/arraynone.md)
* [ArrayPop](/boxlang-language/reference/built-in-functions/array/arraypop.md)
* [ArrayPrepend](/boxlang-language/reference/built-in-functions/array/arrayprepend.md)
* [ArrayPush](/boxlang-language/reference/built-in-functions/array/arraypush.md)
* [ArrayRange](/boxlang-language/reference/built-in-functions/array/arrayrange.md)
* [ArrayReduce](/boxlang-language/reference/built-in-functions/array/arrayreduce.md)
* [ArrayReduceRight](/boxlang-language/reference/built-in-functions/array/arrayreduceright.md)
* [ArrayReject](/boxlang-language/reference/built-in-functions/array/arrayreject.md)
* [ArrayResize](/boxlang-language/reference/built-in-functions/array/arrayresize.md)
* [ArrayReverse](/boxlang-language/reference/built-in-functions/array/arrayreverse.md)
* [ArraySet](/boxlang-language/reference/built-in-functions/array/arrayset.md)
* [ArrayShift](/boxlang-language/reference/built-in-functions/array/arrayshift.md)
* [ArraySlice](/boxlang-language/reference/built-in-functions/array/arrayslice.md)
* [ArraySome](/boxlang-language/reference/built-in-functions/array/arraysome.md)
* [ArraySort](/boxlang-language/reference/built-in-functions/array/arraysort.md)
* [ArraySplice](/boxlang-language/reference/built-in-functions/array/arraysplice.md)
* [ArraySum](/boxlang-language/reference/built-in-functions/array/arraysum.md)
* [ArraySwap](/boxlang-language/reference/built-in-functions/array/arrayswap.md)
* [ArrayToList](/boxlang-language/reference/built-in-functions/array/arraytolist.md)
* [ArrayToStruct](/boxlang-language/reference/built-in-functions/array/arraytostruct.md)
* [ArrayTranspose](/boxlang-language/reference/built-in-functions/array/arraytranspose.md)
* [ArrayUnique](/boxlang-language/reference/built-in-functions/array/arrayunique.md)
* [ArrayUnshift](/boxlang-language/reference/built-in-functions/array/arrayunshift.md)
* [ArrayZip](/boxlang-language/reference/built-in-functions/array/arrayzip.md)


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