# countIf
> Count the number of truthy elements along one or more [`ndarray`][@stdlib/ndarray/ctor] dimensions.
## Usage
```javascript
var countIf = require( '@stdlib/ndarray/count-if' );
```
#### countIf( x\[, options], predicate\[, thisArg] )
Counts the number of truthy elements along one or more [`ndarray`][@stdlib/ndarray/ctor] dimensions.
```javascript
var array = require( '@stdlib/ndarray/array' );
function clbk( value ) {
return value > 0.0;
}
// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 0.0, 6.0 ] ] ] );
// returns
// Perform reduction:
var out = countIf( x, clbk );
// returns [ 5 ]
```
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 clbk( value ) {
return value > 0.0;
}
// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 0.0, 6.0 ] ] ] );
// returns
// Perform reduction:
var opts = {
'dims': [ 1, 2 ]
};
var out = countIf( x, opts, clbk );
// returns [ 2, 2, 1 ]
```
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 clbk( value ) {
return value > 0.0;
}
// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 0.0, 6.0 ] ] ] );
// returns
// Perform reduction:
var opts = {
'dims': [ 1, 2 ],
'keepdims': true
};
var out = countIf( x, opts, clbk );
// returns [ [ [ 2 ] ], [ [ 2 ] ], [ [ 1 ] ] ]
```
To set the predicate function execution context, provide a `thisArg`.
```javascript
var array = require( '@stdlib/ndarray/array' );
function clbk( value ) {
this.count += 1;
return value > 0.0;
}
// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 0.0, 6.0 ] ] ] );
// returns
// Create a context object:
var ctx = {
'count': 0
};
// Perform reduction:
var out = countIf( x, clbk, ctx );
// returns [ 5 ]
var count = ctx.count;
// returns 6
```
#### countIf.assign( x, out\[, options], predicate\[, thisArg] )
Counts the number of truthy elements along one or more [`ndarray`][@stdlib/ndarray/ctor] dimensions and assigns results to a provided output [`ndarray`][@stdlib/ndarray/ctor].
```javascript
var array = require( '@stdlib/ndarray/array' );
var empty = require( '@stdlib/ndarray/empty' );
function clbk( value ) {
return value > 0.0;
}
// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 0.0, 6.0 ] ] ] );
// returns
// Create an output ndarray:
var y = empty( [], {
'dtype': 'int32'
});
// Perform reduction:
var out = countIf.assign( x, y, clbk );
// returns [ 5 ]
var bool = ( out === y );
// returns true
```
The function accepts the following arguments:
- **x**: input [`ndarray`][@stdlib/ndarray/ctor].
- **out**: 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 clbk( value ) {
return value > 0.0;
}
// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 0.0, 6.0 ] ] ] );
// returns
// Create an output ndarray:
var y = empty( [ 3 ], {
'dtype': 'int32'
});
// Perform reduction:
var opts = {
'dims': [ 1, 2 ]
};
var out = countIf.assign( x, y, opts, clbk );
// returns [ 2, 2, 1 ]
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 bernoulli = require( '@stdlib/random/base/bernoulli' ).factory;
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var fillBy = require( '@stdlib/ndarray/fill-by' );
var zeros = require( '@stdlib/ndarray/zeros' );
var isPositiveNumber = require( '@stdlib/assert/is-positive-number' ).isPrimitive;
var countIf = require( '@stdlib/ndarray/count-if' );
var x = zeros( [ 2, 4, 5 ], {
'dtype': 'float64'
});
x = fillBy( x, bernoulli( 0.90 ) );
console.log( ndarray2array( x ) );
var y = countIf( x, isPositiveNumber );
console.log( 'countIf(x[:,:,:]) =' );
console.log( y.get() );
var opts = {
'dims': [ 0 ],
'keepdims': true
};
y = countIf( x, opts, isPositiveNumber );
console.log( 'countIf(x[:,j,k]) =' );
console.log( ndarray2array( y ) );
opts = {
'dims': [ 1 ],
'keepdims': true
};
y = countIf( x, opts, isPositiveNumber );
console.log( 'countIf(x[i,:,k]) =' );
console.log( ndarray2array( y ) );
opts = {
'dims': [ 2 ],
'keepdims': true
};
y = countIf( x, opts, isPositiveNumber );
console.log( 'countIf(x[i,j,:]) =' );
console.log( ndarray2array( y ) );
opts = {
'dims': [ 0, 1 ],
'keepdims': true
};
y = countIf( x, opts, isPositiveNumber );
console.log( 'countIf(x[:,:,k]) =' );
console.log( ndarray2array( y ) );
opts = {
'dims': [ 0, 2 ],
'keepdims': true
};
y = countIf( x, opts, isPositiveNumber );
console.log( 'countIf(x[:,j,:]) =' );
console.log( ndarray2array( y ) );
opts = {
'dims': [ 1, 2 ],
'keepdims': true
};
y = countIf( x, opts, isPositiveNumber );
console.log( 'countIf(x[i,:,:]) =' );
console.log( ndarray2array( y ) );
opts = {
'dims': [ 0, 1, 2 ],
'keepdims': true
};
y = countIf( x, opts, isPositiveNumber );
console.log( 'countIf(x[:,:,:]) =' );
console.log( ndarray2array( y ) );
```
[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/ndarray/tree/main/ctor