# anyBy
> Test whether at least one element along one or more [`ndarray`][@stdlib/ndarray/ctor] dimensions passes a test implemented by a predicate function.
## Usage
```javascript
var anyBy = require( '@stdlib/ndarray/any-by' );
```
#### anyBy( x\[, options], predicate\[, thisArg] )
Tests whether at least one element along one or more [`ndarray`][@stdlib/ndarray/ctor] dimensions passes a test implemented by a predicate function.
```javascript
var array = require( '@stdlib/ndarray/array' );
function isPositive( value ) {
return value > 0.0;
}
// Create an input ndarray:
var x = array( [ [ 1.0, -2.0 ], [ 3.0, -4.0 ] ] );
// Test whether at least one element is positive:
var out = anyBy( x, isPositive );
// returns [ true ]
```
The function accepts the following arguments:
- **x**: input [`ndarray`][@stdlib/ndarray/ctor].
- **options**: function options _(optional)_.
- **predicate**: predicate function.
- **thisArg**: predicate function execution context _(optional)_.
The function accepts the following options:
- **dims**: list of dimensions over which to perform a reduction.
- **keepdims**: boolean indicating whether the reduced dimensions should be included in the returned [`ndarray`][@stdlib/ndarray/ctor] as singleton dimensions. Default: `false`.
By default, the function performs a reduction over all elements in a provided [`ndarray`][@stdlib/ndarray/ctor]. To reduce specific dimensions, set the `dims` option.
```javascript
var array = require( '@stdlib/ndarray/array' );
function isPositive( value ) {
return value > 0.0;
}
// Create an input ndarray:
var x = array( [ [ 1.0, 2.0 ], [ -3.0, -4.0 ] ] );
// returns
var opts = {
'dims': [ 1 ]
};
// Perform reduction:
var out = anyBy( x, opts, isPositive );
// returns [ true, false ]
```
By default, the function returns an [`ndarray`][@stdlib/ndarray/ctor] having a shape matching only the non-reduced dimensions of the input [`ndarray`][@stdlib/ndarray/ctor] (i.e., the reduced dimensions are dropped). To include the reduced dimensions as singleton dimensions in the output [`ndarray`][@stdlib/ndarray/ctor], set the `keepdims` option to `true`.
```javascript
var array = require( '@stdlib/ndarray/array' );
function isPositive( value ) {
return value > 0.0;
}
// Create an input ndarray:
var x = array( [ [ 1.0, 2.0 ], [ -3.0, -4.0 ] ] );
var opts = {
'keepdims': true
};
// Perform reduction:
var out = anyBy( x, opts, isPositive );
// returns [ [ true ] ]
```
To set the function execution context, provide a `thisArg`.
```javascript
var array = require( '@stdlib/ndarray/array' );
function isPositive( value ) {
this.count += 1;
return value > 0.0;
}
// Create an input ndarray:
var x = array( [ [ -1.0, -2.0 ], [ -3.0, 4.0 ] ] );
// returns
// Create a context object:
var ctx = {
'count': 0
};
// Perform reduction:
var out = anyBy( x, isPositive, ctx );
// returns [ true ]
var count = ctx.count;
// returns 4
```
#### anyBy.assign( x, y\[, options], predicate\[, thisArg] )
Tests whether at least one element along one or more [`ndarray`][@stdlib/ndarray/ctor] dimensions passes a test implemented by a predicate function and assigns the result to a provided output [`ndarray`][@stdlib/ndarray/ctor].
```javascript
var array = require( '@stdlib/ndarray/array' );
var empty = require( '@stdlib/ndarray/empty' );
function isPositive( value ) {
return value > 0.0;
}
// Create an input ndarray:
var x = array( [ [ 1.0, -2.0 ], [ 3.0, -4.0 ] ] );
// Create an output ndarray:
var y = empty( [], {
'dtype': 'bool'
});
// Perform reduction:
var out = anyBy.assign( x, y, isPositive );
// returns [ true ]
var bool = ( out === y );
// returns true
```
The function accepts the following arguments:
- **x**: input [`ndarray`][@stdlib/ndarray/ctor].
- **y**: output [`ndarray`][@stdlib/ndarray/ctor]. The output [`ndarray`][@stdlib/ndarray/ctor] must have a shape matching the non-reduced dimensions of the input [`ndarray`][@stdlib/ndarray/ctor].
- **options**: function options _(optional)_.
- **predicate**: predicate function.
- **thisArg**: predicate function execution context _(optional)_.
The function accepts the following options:
- **dims**: list of dimensions over which to perform a reduction.
By default, the function performs a reduction over all elements in a provided [`ndarray`][@stdlib/ndarray/ctor]. To reduce specific dimensions, set the `dims` option.
```javascript
var array = require( '@stdlib/ndarray/array' );
var empty = require( '@stdlib/ndarray/empty' );
function predicate( value ) {
return value > 0.0;
}
// Create an input ndarray:
var x = array( [ [ 1.0, 2.0 ], [ -3.0, -4.0 ] ] );
// returns
// Create an output ndarray:
var y = empty( [ 2 ], {
'dtype': 'bool'
});
var opts = {
'dims': [ 1 ]
};
// Perform reduction:
var out = anyBy.assign( x, y, opts, predicate );
// returns [ true, false ]
var bool = ( out === y );
// returns true
```
## Notes
- The predicate function is provided the following arguments:
- **value**: current array element.
- **indices**: current array element indices.
- **arr**: the input ndarray.
## Examples
```javascript
var discreteUniform = require( '@stdlib/random/base/discrete-uniform' ).factory;
var isEven = require( '@stdlib/assert/is-even' ).isPrimitive;
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var fillBy = require( '@stdlib/ndarray/fill-by' );
var zeros = require( '@stdlib/ndarray/zeros' );
var anyBy = require( '@stdlib/ndarray/any-by' );
var x = zeros( [ 2, 4, 5 ], {
'dtype': 'float64'
});
x = fillBy( x, discreteUniform( 0, 10 ) );
console.log( ndarray2array( x ) );
var y = anyBy( x, isEven );
console.log( y.get() );
```
[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/ndarray/tree/main/ctor