README.md

dnancount

Calculate the number of non-NaN elements in a double-precision floating-point strided array.

Usage

var dnancount = require( '@stdlib/stats/strided/dnancount' );

dnancount( N, x, strideX )

Computes the number of non-NaN elements in a double-precision floating-point strided array x.

var Float64Array = require( '@stdlib/array/float64' );

var x = new Float64Array( [ 1.0, -2.0, NaN, 2.0 ] );

var v = dnancount( x.length, x, 1 );
// returns 3

The function has the following parameters:

• N: number of indexed elements.
• x: input Float64Array.
• strideX: stride length for x.

The N and stride parameters determine which elements in the strided array are accessed at runtime. For example, to count every other element in x,

var Float64Array = require( '@stdlib/array/float64' );

var x = new Float64Array( [ 1.0, 2.0, NaN, -2.0, 4.0, 3.0, NaN, NaN ] );

var v = dnancount( 4, x, 2 );
// returns 2

Note that indexing is relative to the first index. To introduce an offset, use typed array views.

var Float64Array = require( '@stdlib/array/float64' );

var x0 = new Float64Array( [ 2.0, 1.0, NaN, -2.0, 3.0, 4.0, NaN, NaN ] );
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

var v = dnancount( 4, x1, 2 );
// returns 3

dnancount.ndarray( N, x, strideX, offsetX )

Computes the number of non-NaN elements in a double-precision floating-point strided array using alternative indexing semantics.

var Float64Array = require( '@stdlib/array/float64' );

var x = new Float64Array( [ 2.0, 1.0, -2.0, -2.0, 3.0, 4.0, NaN, NaN ] );

var v = dnancount.ndarray( 4, x, 2, 1 );
// returns 3

The function has the following additional parameter:

• offsetX: starting index for x.

While typed array views mandate a view offset based on the underlying buffer, the offset parameter supports indexing semantics based on a starting index. For example, to count every other element in x starting from the second element,

var Float64Array = require( '@stdlib/array/float64' );

var x = new Float64Array( [ 2.0, 1.0, NaN, -2.0, 3.0, 4.0, NaN, NaN ] );

var v = dnancount.ndarray( 4, x, 2, 1 );
// returns 3

Notes

• If N <= 0, both functions return 0.
• If strideX == 0, the same indexed element is evaluated N times.
• The C APIs return CBLAS_INT.

Examples

var uniform = require( '@stdlib/random/base/uniform' );
var filledarrayBy = require( '@stdlib/array/filled-by' );
var bernoulli = require( '@stdlib/random/base/bernoulli' );
var dnancount = require( '@stdlib/stats/strided/dnancount' );

function rand() {
    if ( bernoulli( 0.2 ) < 1 ) {
        return NaN;
    }
    return uniform( -50.0, 50.0 );
}

var x = filledarrayBy( 10, 'float64', rand );
console.log( x );

var v = dnancount( x.length, x, 1 );
console.log( v );

---

C APIs

Usage

#include "stdlib/stats/strided/dnancount.h"

stdlib_strided_dnancount( N, *X, strideX )

Computes the number of non-NaN elements in a double-precision floating-point strided array.

CBLAS_INT stdlib_strided_dnancount( const CBLAS_INT N, const double *X, const CBLAS_INT strideX );

The function accepts the following arguments:

• N: [in] CBLAS_INT number of indexed elements.
• X: [in] double* input array.
• strideX: [in] CBLAS_INT stride length for X.

const double x[] = { 1.0, 2.0, NaN, 4.0, 5.0, 6.0, NaN, 8.0 };

CBLAS_INT v = stdlib_strided_dnancount( 4, x, 2 );
// returns 2

stdlib_strided_dnancount_ndarray( N, *X, strideX, offsetX )

Computes the number of non-NaN elements in a double-precision floating-point strided array using alternative indexing semantics.

CBLAS_INT stdlib_strided_dnancount_ndarray( const CBLAS_INT N, const double *X, const CBLAS_INT strideX, const CBLAS_INT offsetX );

The function accepts the following additional argument:

• offsetX: [in] CBLAS_INT starting index for X.

const double x[] = { 2.0, 1.0, NaN, -2.0, 3.0, 4.0, NaN, NaN };

CBLAS_INT v = stdlib_strided_dnancount_ndarray( 4, x, 2, 1 );
// returns 3

Notes

• If N <= 0, both functions return 0.

Examples

#include "stdlib/stats/strided/dnancount.h"
#include <stdint.h>
#include <stdio.h>

int main( void ) {
    const double x[] = { 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 0.0/0.0, 0.0/0.0 };
    const int N = 5;
    const int strideX = 2;

    CBLAS_INT v = stdlib_strided_dnancount( N, x, strideX );

    printf( "count: %d\n", (int)v );
}