# find
> Return the first element in an ndarray which passes a test implemented by a predicate function.
## Usage
```javascript
var find = require( '@stdlib/ndarray/base/find' );
```
#### find( arrays, predicate\[, thisArg] )
Returns the first element in an ndarray which passes a test implemented by a predicate function.
```javascript
var Float64Array = require( '@stdlib/array/float64' );
function isEven( value ) {
return value % 2.0 === 0.0;
}
// Create a data buffer:
var xbuf = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );
// Define the shape of the input array:
var shape = [ 3, 1, 2 ];
// Define the array strides:
var sx = [ 4, 4, 1 ];
// Define the index offset:
var ox = 0;
// Create the input ndarray-like object:
var x = {
'dtype': 'float64',
'data': xbuf,
'shape': shape,
'strides': sx,
'offset': ox,
'order': 'row-major'
};
// Create an ndarray-like object containing a sentinel value:
var sentinelValue = {
'dtype': 'float64',
'data': new Float64Array( [ NaN ] ),
'shape': [],
'strides': [ 0 ],
'offset': 0,
'order': 'row-major'
};
// Perform reduction:
var out = find( [ x, sentinelValue ], isEven );
// returns 2.0
```
The function accepts the following arguments:
- **arrays**: array-like object containing an input ndarray and a zero-dimensional ndarray containing a sentinel value. The sentinel value is returned when no element in an input ndarray passes a test implemented by the predicate function.
- **predicate**: predicate function.
- **thisArg**: predicate function execution context (_optional_).
To set the predicate function execution context, provide a `thisArg`.
```javascript
var Float64Array = require( '@stdlib/array/float64' );
function isEven( value ) {
this.count += 1;
return value % 2.0 === 0.0;
}
// Create a data buffer:
var xbuf = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );
// Define the shape of the input array:
var shape = [ 3, 1, 2 ];
// Define the array strides:
var sx = [ 4, 4, 1 ];
// Define the index offset:
var ox = 0;
// Create the input ndarray-like object:
var x = {
'dtype': 'float64',
'data': xbuf,
'shape': shape,
'strides': sx,
'offset': ox,
'order': 'row-major'
};
// Create an ndarray-like object containing a sentinel value:
var sentinelValue = {
'dtype': 'float64',
'data': new Float64Array( [ NaN ] ),
'shape': [],
'strides': [ 0 ],
'offset': 0,
'order': 'row-major'
};
var ctx = {
'count': 0
};
// Perform reduction:
var out = find( [ x, sentinelValue ], isEven, ctx );
// returns 2.0
var count = ctx.count;
// returns 2
```
## Notes
- Each provided ndarray should be an object with the following properties:
- **dtype**: data type.
- **data**: data buffer.
- **shape**: dimensions.
- **strides**: stride lengths.
- **offset**: index offset.
- **order**: specifies whether an ndarray is row-major (C-style) or column major (Fortran-style).
- The predicate function is provided the following arguments:
- **value**: current array element.
- **indices**: current array element indices.
- **arr**: the input ndarray.
- For very high-dimensional ndarrays which are non-contiguous, one should consider copying the underlying data to contiguous memory before performing the operation in order to achieve better performance.
## Examples
```javascript
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var Float64Array = require( '@stdlib/array/float64' );
var ndarray2array = require( '@stdlib/ndarray/base/to-array' );
var find = require( '@stdlib/ndarray/base/find' );
function isEven( value ) {
return value % 2.0 === 0.0;
}
var x = {
'dtype': 'float64',
'data': discreteUniform( 10, 0.0, 10.0, {
'dtype': 'float64'
}),
'shape': [ 5, 2 ],
'strides': [ 2, 1 ],
'offset': 0,
'order': 'row-major'
};
console.log( ndarray2array( x.data, x.shape, x.strides, x.offset, x.order ) );
var sv = {
'dtype': 'float64',
'data': new Float64Array( [ NaN ] ),
'shape': [],
'strides': [ 0 ],
'offset': 0,
'order': x.order
};
console.log( 'Sentinel Value: %d', sv.data[ 0 ] );
var out = find( [ x, sv ], isEven );
console.log( out );
```