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README.md

mskmax

Calculate the maximum value of a strided array according to a mask.

Usage

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

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

Computes the maximum value of a strided array according to a mask.

var x = [ 1.0, -2.0, 4.0, 2.0 ];
var mask = [ 0, 0, 1, 0 ];

var v = mskmax( x.length, x, 1, mask, 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.
  • mask: mask Array or typed array. 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: stride length for mask.

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

var x = [ 1.0, 2.0, -7.0, -2.0, 4.0, 3.0, 5.0, 6.0 ];
var mask = [ 0, 0, 0, 0, 0, 0, 1, 1 ];

var v = mskmax( 4, x, 2, mask, 2 );
// returns 4.0

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

var Float64Array = require( '@stdlib/array/float64' );
var Uint8Array = require( '@stdlib/array/uint8' );

var x0 = new Float64Array( [ 2.0, 1.0, -2.0, -2.0, 3.0, 4.0, 5.0, 6.0 ] );
var x1 = new Float64Array( 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 v = mskmax( 4, x1, 2, mask1, 2 );
// returns 4.0

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

Computes the maximum value of a strided array according to a mask and using alternative indexing semantics.

var x = [ 1.0, -2.0, 4.0, 2.0 ];
var mask = [ 0, 0, 1, 0 ];

var v = mskmax.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 parameters support indexing semantics based on starting indices. For example, to calculate the maximum value for every other value in x starting from the second value

var x = [ 2.0, 1.0, -2.0, -2.0, 3.0, 4.0, 5.0, 6.0 ];
var mask = [ 0, 0, 0, 0, 0, 0, 1, 1 ];

var v = mskmax.ndarray( 4, x, 2, 1, mask, 2, 1 );
// returns 4.0

Notes

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

Examples

var uniform = require( '@stdlib/random/array/uniform' );
var bernoulli = require( '@stdlib/random/array/bernoulli' );
var mskmax = require( '@stdlib/stats/strided/mskmax' );

var x = uniform( 10, -50.0, 50.0, {
    'dtype': 'float64'
});
console.log( x );

var mask = bernoulli( x.length, 0.2, {
    'dtype': 'uint8'
});
console.log( mask );

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

See Also