# outputDataType
> Resolve the output ndarray [data type][@stdlib/ndarray/dtypes] from a list of input ndarray [data types][@stdlib/ndarray/dtypes].
## Usage
```javascript
var outputDataType = require( '@stdlib/ndarray/base/output-dtype' );
```
#### outputDataType( dtypes, policy )
Resolves the output ndarray [data type][@stdlib/ndarray/dtypes] from a list of input ndarray [data types][@stdlib/ndarray/dtypes] according to a [data type policy][@stdlib/ndarray/output-dtype-policies].
```javascript
var dt = outputDataType( [ 'int32', 'uint32' ], 'floating_point' );
// returns 'float64'
```
The function supports the following parameters:
- **dtypes**: list of input ndarray [data types][@stdlib/ndarray/dtypes].
- **policy**: output [data type policy][@stdlib/ndarray/output-dtype-policies].
If `policy` is a [data type][@stdlib/ndarray/dtypes], the function always returns the `policy` value (i.e., the second argument).
```javascript
var dt = outputDataType( [ 'float32', 'float32' ], 'float64' );
// returns 'float64'
dt = outputDataType( [ 'int32', 'complex128' ], 'float64' );
// returns 'float64'
// ...
```
## Notes
- When provided more than [data type][@stdlib/ndarray/dtypes], the function **always** applies [type promotion][@stdlib/ndarray/promotion-rules] to the provided data types, except for the following [data type policies][@stdlib/ndarray/output-dtype-policies]:
- `default`
- `default_index`
- `same`
- ``
## Examples
```javascript
var naryFunction = require( '@stdlib/utils/nary-function' );
var unzip = require( '@stdlib/utils/unzip' );
var cartesianProduct = require( '@stdlib/array/base/cartesian-product' );
var dtypes = require( '@stdlib/ndarray/dtypes' );
var logEachMap = require( '@stdlib/console/log-each-map' );
var outputDataType = require( '@stdlib/ndarray/base/output-dtype' );
// Get the list of real-valued data types:
var dt = dtypes( 'real' );
// Define a list of output data type policies:
var policies = [
'default',
'real',
'floating_point',
'complex_floating_point',
'promoted'
];
// Generate data type pairs:
var pairs = cartesianProduct( dt, dt );
// Generate argument pairs:
var args = cartesianProduct( pairs, policies );
// Unzip the argument pair array:
args = unzip( args );
// Resolve output data types:
logEachMap( 'dtypes: (%15s). policy: %-24s. output dtype: %s.', args[ 0 ], args[ 1 ], naryFunction( outputDataType, 2 ) );
```
[@stdlib/ndarray/dtypes]: https://github.com/stdlib-js/ndarray/tree/main/dtypes
[@stdlib/ndarray/output-dtype-policies]: https://github.com/stdlib-js/ndarray/tree/main/output-dtype-policies
[@stdlib/ndarray/promotion-rules]: https://github.com/stdlib-js/ndarray/tree/main/promotion-rules