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README.md

nanmaxabs

Calculate the maximum absolute value of a strided array, ignoring NaN values.

Usage

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

nanmaxabs( N, x, strideX )

Computes the maximum absolute value of a strided array, ignoring NaN values.

var x = [ 1.0, -2.0, NaN, 2.0 ];

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

The function has the following parameters:

  • N: number of indexed elements.
  • x: input Array or typed array.
  • strideX: stride length for x.

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

var x = [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0, NaN, NaN ];

var v = nanmaxabs( 5, x, 2 );
// returns 4.0

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

var v = nanmaxabs( 4, x1, 2 );
// returns 4.0

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

Computes the maximum absolute value of a strided array, ignoring NaN values and using alternative indexing semantics.

var x = [ 1.0, -2.0, NaN, 2.0 ];

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

The function has the following additional parameters:

  • 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 calculate the maximum absolute value for every other element in x starting from the second element

var x = [ 2.0, 1.0, 2.0, -2.0, -2.0, NaN, NaN, 2.0, 3.0, 4.0 ];

var v = nanmaxabs.ndarray( 5, x, 2, 1 );
// returns 4.0

Notes

  • If N <= 0, both functions return NaN.
  • Both functions support array-like objects having getter and setter accessors for array element access (e.g., @stdlib/array/base/accessor).
  • Depending on the environment, the typed versions (dnanmaxabs, snanmaxabs, etc.) are likely to be significantly more performant.

Examples

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

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

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

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

See Also