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README.md

find

Return a new ndarray containing the first elements which pass a test implemented by a predicate function along one or more ndarray dimensions.

Usage

var find = require( '@stdlib/ndarray/find' );

find( x[, options], predicate[, thisArg] )

Returns a new ndarray containing the first elements which pass a test implemented by a predicate function along one or more ndarray dimensions.

var array = require( '@stdlib/ndarray/array' );

function isEven( value ) {
    return value % 2.0 === 0.0;
}

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
// returns <ndarray>

// Perform reduction:
var out = find( x, isEven );
// returns <ndarray>

var v = out.get();
// returns 2.0

The function accepts the following arguments:

  • x: input ndarray.
  • 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 as singleton dimensions. Default: false.
  • sentinelValue: value to return when no element passes the test. May be either a scalar value or a zero-dimensional ndarray.

By default, the function performs reduction over all all elements in a provided ndarray. To reduce specific dimensions, set the dims option.

var array = require( '@stdlib/ndarray/array' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );

function isEven( value ) {
    return value % 2.0 === 0.0;
}

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
// returns <ndarray>

var opts = {
    'dims': [ 0 ]
};

// Perform reduction:
var out = find( x, opts, isEven );
// returns <ndarray>

var v = ndarray2array( out );
// returns [ [ NaN, 2.0 ], [ NaN, 4.0 ] ]

By default, the function returns an ndarray having a shape matching only the non-reduced dimensions of the input ndarray (i.e., the reduced dimensions are dropped). To include the reduced dimensions as singleton dimensions in the output ndarray, set the keepdims option to true.

var array = require( '@stdlib/ndarray/array' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );

function isEven( value ) {
    return value % 2.0 === 0.0;
}

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
// returns <ndarray>

var opts = {
    'dims': [ 0 ],
    'keepdims': true
};

// Perform reduction:
var out = find( x, opts, isEven );
// returns <ndarray>

var v = ndarray2array( out );
// returns [ [ [ NaN, 2 ], [ NaN, 4 ] ] ]

To specify a custom sentinel value to return when no element passes the test, set the sentinelValue option.

var array = require( '@stdlib/ndarray/array' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );

function isEven( value ) {
    return value % 2.0 === 0.0;
}

// Create an input ndarray:
var x = array( [ [ [ 1.0, 3.0 ], [ 5.0, 7.0 ] ], [ [ 9.0, 11.0 ], [ 13.0, 15.0 ] ] ] );
// returns <ndarray>

var opts = {
    'sentinelValue': -999
};

// Perform reduction:
var out = find( x, opts, isEven );
// returns <ndarray>

var v = out.get();
// returns -999

To set the predicate function execution context, provide a thisArg.

var array = require( '@stdlib/ndarray/array' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );

function isEven( value ) {
    this.count += 1;
    return value % 2.0 === 0.0;
}

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
// returns <ndarray>

var ctx = {
    'count': 0
};

// Perform reduction:
var out = find( x, isEven, ctx );
// returns <ndarray>

var v = out.get();
// returns 2.0

var count = ctx.count;
// returns 2

find.assign( x, out[, options], predicate[, thisArg] )

Finds the first elements which pass a test implemented by a predicate function along one or more ndarray dimensions and assigns results to a provided output ndarray.

var array = require( '@stdlib/ndarray/array' );
var empty = require( '@stdlib/ndarray/empty' );

function isEven( value ) {
    return value % 2.0 === 0.0;
}

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
// returns <ndarray>

// Create an output ndarray:
var y = empty( [], {
    'dtype': x.dtype
});

// Perform reduction:
var out = find.assign( x, y, isEven );
// returns <ndarray>

var bool = ( out === y );
// returns true

var v = y.get();
// returns 2.0

The function accepts the following arguments:

  • x: input ndarray.
  • out: output ndarray.
  • 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.
  • sentinelValue: value to return when no element passes the test. May be either a scalar value or a zero-dimensional ndarray.
var array = require( '@stdlib/ndarray/array' );
var empty = require( '@stdlib/ndarray/empty' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );

function isEven( value ) {
    return value % 2.0 === 0.0;
}

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ], [ 7.0, 8.0 ] ] ] );
// returns <ndarray>

// Create an output ndarray:
var y = empty( [ 2, 2 ], {
    'dtype': x.dtype
});

var opts = {
    'dims': [ 0 ]
};

// Perform reduction:
var out = find.assign( x, y, opts, isEven );

var bool = ( out === y );
// returns true

var v = ndarray2array( y );
// returns [ [ NaN, 2.0 ], [ NaN, 4.0 ] ]

Notes

  • By default, when no sentinelValue is provided, the function returns a default sentinel value based on the input ndarray data-type:

    • real-valued floating-point data types: NaN.
    • complex-valued floating-point data types: NaN + NaNj.
    • integer data types: maximum value.
    • boolean data types: false.

  • The predicate function is provided the following arguments:

    • value: current array element.
    • indices: current array element indices.
    • arr: the input ndarray.

Examples

var uniform = require( '@stdlib/random/uniform' );
var isPositive = require( '@stdlib/assert/is-positive-number' ).isPrimitive;
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var find = require( '@stdlib/ndarray/find' );

var x = uniform( [ 2, 4, 5 ], -10.0, 10.0, {
    'dtype': 'float64'
});
console.log( ndarray2array( x ) );

var y = find( x, isPositive );
console.log( y.get() );