# flatten
> Return a flattened copy of an input [ndarray][@stdlib/ndarray/ctor].
## Usage
```javascript
var flatten = require( '@stdlib/ndarray/flatten' );
```
#### flatten( x\[, options] )
Returns a flattened copy of an input [ndarray][@stdlib/ndarray/ctor].
```javascript
var array = require( '@stdlib/ndarray/array' );
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ] ] ] );
// returns
var y = flatten( x );
// returns [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ]
```
The function accepts the following arguments:
- **x**: input [ndarray][@stdlib/ndarray/ctor].
- **options**: function options (_optional_).
The function accepts the following options:
- **order**: order in which input [ndarray][@stdlib/ndarray/ctor] elements should be flattened. Must be one of the following:
- `'row-major'`: flatten elements in lexicographic order. For example, given a two-dimensional input [ndarray][@stdlib/ndarray/ctor] (i.e., a matrix), flattening in lexicographic order means flattening the input [ndarray][@stdlib/ndarray/ctor] row-by-row.
- `'column-major'`: flatten elements in colexicographic order. For example, given a two-dimensional input [ndarray][@stdlib/ndarray/ctor] (i.e., a matrix), flattening in colexicographic order means flattening the input [ndarray][@stdlib/ndarray/ctor] column-by-column.
- `'any'`: flatten according to the physical layout of the input [ndarray][@stdlib/ndarray/ctor] data in memory, regardless of the stated [order][@stdlib/ndarray/orders] of the input [ndarray][@stdlib/ndarray/ctor].
- `'same'`: flatten according to the stated [order][@stdlib/ndarray/orders] of the input [ndarray][@stdlib/ndarray/ctor].
Default: `'row-major'`.
- **depth**: maximum number of input [ndarray][@stdlib/ndarray/ctor] dimensions to flatten.
- **dtype**: output ndarray [data type][@stdlib/ndarray/dtypes]. By default, the function returns an [ndarray][@stdlib/ndarray/ctor] having the same [data type][@stdlib/ndarray/dtypes] as a provided input [ndarray][@stdlib/ndarray/ctor].
By default, the function flattens all dimensions of the input [ndarray][@stdlib/ndarray/ctor]. To flatten to a desired depth, specify the `depth` option.
```javascript
var array = require( '@stdlib/ndarray/array' );
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ] ] ] );
// returns
var y = flatten( x, {
'depth': 1
});
// returns [ [ 1.0, 2.0 ], [ 3.0, 4.0 ], [ 5.0, 6.0 ] ]
```
By default, the input [ndarray][@stdlib/ndarray/ctor] is flattened in lexicographic order. To flatten elements in a different order, specify the `order` option.
```javascript
var array = require( '@stdlib/ndarray/array' );
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ] ] ] );
// returns
var y = flatten( x, {
'order': 'column-major'
});
// returns [ 1.0, 3.0, 5.0, 2.0, 4.0, 6.0 ]
```
By default, the output ndarray [data type][@stdlib/ndarray/dtypes] is inferred from the input [ndarray][@stdlib/ndarray/ctor]. To return an ndarray with a different [data type][@stdlib/ndarray/dtypes], specify the `dtype` option.
```javascript
var array = require( '@stdlib/ndarray/array' );
var dtype = require( '@stdlib/ndarray/dtype' );
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ] ] ] );
// returns
var y = flatten( x, {
'dtype': 'float32'
});
// returns [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ]
var dt = String( dtype( y ) );
// returns 'float32'
```
## Notes
- The function **always** returns a copy of input [ndarray][@stdlib/ndarray/ctor] data, even when an input [ndarray][@stdlib/ndarray/ctor] already has the desired number of dimensions.
## Examples
```javascript
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var array = require( '@stdlib/ndarray/array' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var flatten = require( '@stdlib/ndarray/flatten' );
var xbuf = discreteUniform( 12, -100, 100, {
'dtype': 'generic'
});
var x = array( xbuf, {
'shape': [ 2, 2, 3 ],
'dtype': 'generic'
});
console.log( ndarray2array( x ) );
var y = flatten( x );
console.log( ndarray2array( y ) );
```
[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/ndarray/tree/main/ctor
[@stdlib/ndarray/dtypes]: https://github.com/stdlib-js/ndarray/tree/main/dtypes
[@stdlib/ndarray/orders]: https://github.com/stdlib-js/ndarray/tree/main/orders