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snanmean

README.md

snanmean

Calculate the arithmetic mean of a single-precision floating-point strided array, ignoring NaN values.

The arithmetic mean is defined as

$$\mu = \frac{1}{n} \sum_{i=0}^{n-1} x_i$$

Usage

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

snanmean( N, x, strideX )

Computes the arithmetic mean of a single-precision floating-point strided array, ignoring NaN values.

var Float32Array = require( '@stdlib/array/float32' );

var x = new Float32Array( [ 1.0, -2.0, NaN, 2.0 ] );

var v = snanmean( x.length, x, 1 );
// returns ~0.3333

The function has the following parameters:

  • N: number of indexed elements.
  • x: input Float32Array.
  • strideX: stride length.

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

var Float32Array = require( '@stdlib/array/float32' );

var x = new Float32Array( [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0, NaN ] );

var v = snanmean( 4, x, 2 );
// returns 1.25

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

var Float32Array = require( '@stdlib/array/float32' );

var x0 = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0, NaN, NaN ] );
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

var v = snanmean( 5, x1, 2 );
// returns 1.25

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

Computes the arithmetic mean of a single-precision floating-point strided array, ignoring NaN values and using alternative indexing semantics.

var Float32Array = require( '@stdlib/array/float32' );

var x = new Float32Array( [ 1.0, -2.0, NaN, 2.0 ] );

var v = snanmean.ndarray( x.length, x, 1, 0 );
// returns ~0.33333

The function has the following additional parameters:

  • offsetX: starting index.

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 calculate the arithmetic mean for every other element in x starting from the second element

var Float32Array = require( '@stdlib/array/float32' );

var x = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0, NaN, NaN ] );

var v = snanmean.ndarray( 5, x, 2, 1 );
// returns 1.25

Notes

  • If N <= 0, both functions return NaN.
  • If every indexed element is NaN, both functions return NaN.

Examples

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

function rand() {
    if ( bernoulli( 0.8 ) < 1 ) {
        return NaN;
    }
    return uniform( -50.0, 50.0 );
}

var x = filledarrayBy( 10, 'float32', rand );
console.log( x );

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

C APIs

Usage

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

stdlib_strided_snanmean( N, *X, strideX )

Computes the arithmetic mean of a single-precision floating-point strided array, ignoring NaN values.

const float x[] = { 1.0f, 2.0f, 3.0f, 0.0f/0.0f };

float v = stdlib_strided_snanmean( 4, x, 1 );
// returns 2.0f

The function accepts the following arguments:

  • N: [in] CBLAS_INT number of indexed elements.
  • X: [in] float* input array.
  • strideX: [in] CBLAS_INT stride length.
float stdlib_strided_snanmean( const CBLAS_INT N, const float *X, const CBLAS_INT strideX );

stdlib_strided_snanmean_ndarray( N, *X, strideX, offsetX )

Computes the arithmetic mean of a single-precision floating-point strided array, ignoring NaN values and using alternative indexing semantics.

const float x[] = { 1.0f, 2.0f, 3.0f, 0.0f/0.0f };

float v = stdlib_strided_snanmean_ndarray( 4, x, 1, 0 );
// returns 2.0f

The function accepts the following arguments:

  • N: [in] CBLAS_INT number of indexed elements.
  • X: [in] float* input array.
  • strideX: [in] CBLAS_INT stride length.
  • offsetX: [in] CBLAS_INT starting index.
float stdlib_strided_snanmean_ndarray( const CBLAS_INT N, const float *X, const CBLAS_INT strideX, const CBLAS_INT offsetX );

Examples

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

int main( void ) {
    // Create a strided array:
    const float x[] = { 1.0f, 2.0f, 0.0f/0.0f, 3.0f, 0.0f/0.0f, 4.0f, 5.0f, 6.0f, 0.0f/0.0f, 7.0f, 8.0f, 0.0f/0.0f };

    // Specify the number of elements:
    const int N = 6;

    // Specify the stride length:
    const int strideX = 2;

    // Compute the arithmetic mean:
    float v = stdlib_strided_snanmean( N, x, strideX );

    // Print the result:
    printf( "mean: %f\n", v );
}

See Also