Usage

`javascript
var findIndex = require( '@stdlib/blas-ext-find-index' );
`

#### findIndex( x\[, options], clbk\[, thisArg] )

Returns the index of the first element along an [ndarray][@stdlib/ndarray/ctor] dimension which passes a test implemented by a predicate function.

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

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

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

// Perform operation:
var out = findIndex( x, isEven );
// returns

var idx = out.get();
// returns 1
`

The function has the following parameters:

- x: input [ndarray][@stdlib/ndarray/ctor]. Must have at least one dimension.
- options: function options (_optional_).
- clbk: callback function.
- thisArg: callback execution context (_optional_).

The invoked callback is provided three arguments:

- value: current array element.
- idx: current array element index.
- array: input ndarray.

To set the callback execution context, provide a thisArg.

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

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

var x = array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );

var ctx = {
'count': 0
};
var out = findIndex( x, isEven, ctx );
// returns

var idx = out.get();
// returns 1

var count = ctx.count;
// returns 2
`

The function accepts the following options:

- dtype: output ndarray [data type][@stdlib/ndarray/dtypes]. Must be an integer index or generic [data type][@stdlib/ndarray/dtypes].
- dim: dimension over which to perform operation. If provided a negative integer, the dimension along which to perform the operation is determined by counting backward from the last dimension (where -1 refers to the last dimension). Default: -1.
- keepdims: boolean indicating whether the reduced dimensions should be included in the returned [ndarray][@stdlib/ndarray/ctor] as singleton dimensions. Default: false.

If no element along an [ndarray][@stdlib/ndarray/ctor] dimension passes a test implemented by the predicate function, the corresponding element in the returned [ndarray][@stdlib/ndarray/ctor] is -1.

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

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

// Create an input ndarray:
var x = array( [ 1.0, 3.0, 5.0, 7.0 ] );
// returns

// Perform operation:
var out = findIndex( x, isEven );
// returns

var idx = out.get();
// returns -1
`

By default, the function performs the operation over elements in the last dimension. To perform the operation over a different dimension, provide a dim option.

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

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

var x = array( [ [ -1.0, 2.0 ], [ -3.0, 4.0 ] ] );

var opts = {
'dim': 0
};

var out = findIndex( x, opts, isEven );
// returns

var idx = ndarray2array( out );
// returns [ -1, 0 ]
`

By default, the function excludes reduced dimensions from the output [ndarray][@stdlib/ndarray/ctor]. To include the reduced dimensions as singleton dimensions, set the keepdims option to true.

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

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

var x = array( [ [ -1.0, 2.0 ], [ -3.0, 4.0 ] ] );

var opts = {
'dim': 0,
'keepdims': true
};

var out = findIndex( x, opts, isEven );
// returns

var idx = ndarray2array( out );
// returns [ [ -1, 0 ] ]
`

By default, the function returns an [ndarray][@stdlib/ndarray/ctor] having a [data type][@stdlib/ndarray/dtypes] determined by the function's output data type [policy][@stdlib/ndarray/output-dtype-policies]. To override the default behavior, set the dtype option.

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

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

var x = array( [ 1.0, 2.0, 3.0, 4.0 ] );

var opts = {
'dtype': 'generic'
};

var idx = findIndex( x, opts, isEven );
// returns

var dt = dtype( idx );
// returns 'generic'
`

#### findIndex.assign( x, out\[, options], clbk\[, thisArg] )

Returns the index of the first element along an [ndarray][@stdlib/ndarray/ctor] dimension which passes a test implemented by a predicate function and assigns results to a provided output [ndarray][@stdlib/ndarray/ctor].

`javascript
var array = require( '@stdlib/ndarray-array' );
var zeros = require( '@stdlib/ndarray-zeros' );

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

var x = array( [ 1.0, 2.0, 3.0, 4.0 ] );
var y = zeros( [], {
'dtype': 'int32'
});

var out = findIndex.assign( x, y, isEven );
// returns

var idx = out.get();
// returns 1

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

The method has the following parameters:

- x: input [ndarray][@stdlib/ndarray/ctor]. Must have at least one dimension.
- out: output [ndarray][@stdlib/ndarray/ctor].
- options: function options (_optional_).
- clbk: callback function.
- thisArg: callback execution context (_optional_).

The method accepts the following options:

- dim: dimension over which to perform operation. If provided a negative integer, the dimension along which to perform the operation is determined by counting backward from the last dimension (where -1 refers to the last dimension). Default: -1.