smskmax

Calculate the maximum value of a single-precision floating-point strided array according to a mask.

Installation

npm install @stdlib/stats-base-smskmax

Usage

var smskmax = require( '@stdlib/stats-base-smskmax' );

smskmax( N, x, strideX, mask, strideMask )

Computes the maximum value of a single-precision floating-point strided array x according to a mask.

var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );

var x = new Float32Array( [ 1.0, -2.0, 4.0, 2.0 ] );
var mask = new Uint8Array( [ 0, 0, 1, 0 ] );

var v = smskmax( x.length, x, 1, mask, 1 );
// returns 2.0

The function has the following parameters:

• N: number of indexed elements.
• x: input Float32Array.
• strideX: index increment for x.
• mask: mask Uint8Array. If a mask array element is 0, the corresponding element in x is considered valid and included in computation. If a mask array element is 1, the corresponding element in x is considered invalid/missing and excluded from computation.
• strideMask: index increment for mask.

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

var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );
var floor = require( '@stdlib/math-base-special-floor' );

var x = new Float32Array( [ 1.0, 2.0, -7.0, -2.0, 4.0, 3.0, 5.0, 6.0 ] );
var mask = new Uint8Array( [ 0, 0, 0, 0, 0, 0, 1, 1 ] );
var N = floor( x.length / 2 );

var v = smskmax( N, x, 2, mask, 2 );
// returns 4.0

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

var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );
var floor = require( '@stdlib/math-base-special-floor' );

var x0 = new Float32Array( [ 2.0, 1.0, -2.0, -2.0, 3.0, 4.0, 5.0, 6.0 ] );
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

var mask0 = new Uint8Array( [ 0, 0, 0, 0, 0, 0, 1, 1 ] );
var mask1 = new Uint8Array( mask0.buffer, mask0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

var N = floor( x0.length / 2 );

var v = smskmax( N, x1, 2, mask1, 2 );
// returns 4.0

smskmax.ndarray( N, x, strideX, offsetX, mask, strideMask, offsetMask )

Computes the maximum value of a single-precision floating-point strided array according to a mask and using alternative indexing semantics.

var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );

var x = new Float32Array( [ 1.0, -2.0, 4.0, 2.0 ] );
var mask = new Uint8Array( [ 0, 0, 1, 0 ] );

var v = smskmax.ndarray( x.length, x, 1, 0, mask, 1, 0 );
// returns 2.0

The function has the following additional parameters:

• offsetX: starting index for x.
• offsetMask: starting index for mask.

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 maximum value for every other value in x starting from the second value

var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );
var floor = require( '@stdlib/math-base-special-floor' );

var x = new Float32Array( [ 2.0, 1.0, -2.0, -2.0, 3.0, 4.0, 5.0, 6.0 ] );
var mask = new Uint8Array( [ 0, 0, 0, 0, 0, 0, 1, 1 ] );
var N = floor( x.length / 2 );

var v = smskmax.ndarray( N, x, 2, 1, mask, 2, 1 );
// returns 4.0

Notes

• If N <= 0, both functions return NaN.

Examples

var randu = require( '@stdlib/random-base-randu' );
var round = require( '@stdlib/math-base-special-round' );
var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );
var smskmax = require( '@stdlib/stats-base-smskmax' );

var mask;
var x;
var i;

x = new Float32Array( 10 );
mask = new Uint8Array( x.length );
for ( i = 0; i < x.length; i++ ) {
    if ( randu() < 0.2 ) {
        mask[ i ] = 1;
    } else {
        mask[ i ] = 0;
    }
    x[ i ] = round( (randu()*100.0) - 50.0 );
}
console.log( x );
console.log( mask );

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

See Also

• @stdlib/stats-base/dmskmax: calculate the maximum value of a double-precision floating-point strided array according to a mask.
• @stdlib/stats-base/mskmax: calculate the maximum value of a strided array according to a mask.
• @stdlib/stats-base/smax: calculate the maximum value of a single-precision floating-point strided array.
• @stdlib/stats-base/smskmin: calculate the minimum value of a single-precision floating-point strided array according to a mask.
• @stdlib/stats-base/snanmax: calculate the maximum value of a single-precision floating-point strided array, ignoring NaN values.
• @stdlib/stats-base/snanmskmax: calculate the maximum value of a single-precision floating-point strided array according to a mask, ignoring NaN values.

Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

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License

See LICENSE.

Copyright

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