itermprod

Create an iterator which iteratively computes a moving product.

For a window of size W, the moving product is defined as

product Underscript i equals 0 Overscript upper W minus 1 Endscripts x Subscript i

Usage

var itermprod = require( '@stdlib/stats/iter/mprod' );

itermprod( iterator, W )

Returns an iterator which iteratively computes a moving product. The W parameter defines the number of iterated values over which to compute the moving product.

var array2iterator = require( '@stdlib/array/to-iterator' );

var arr = array2iterator( [ 2.0, 1.0, 3.0, -7.0, -5.0 ] );
var it = itermprod( arr, 3 );

// Fill the window...
var p = it.next().value; // [2.0]
// returns 2.0

p = it.next().value; // [2.0, 1.0]
// returns 2.0

p = it.next().value; // [2.0, 1.0, 3.0]
// returns 6.0

// Window begins sliding...
p = it.next().value; // [1.0, 3.0, -7.0]
// returns -21.0

p = it.next().value; // [3.0, -7.0, -5.0]
// returns 105.0

Notes

  • If an iterated value is non-numeric (including NaN), the function returns NaN for at least W-1 future invocations. If non-numeric iterated values are possible, you are advised to provide an iterator which type checks and handles non-numeric values accordingly.
  • As W values are needed to fill the window buffer, the first W-1 returned values are calculated from smaller sample sizes. Until the window is full, each returned value is calculated from all previously iterated values.

Examples

var runif = require( '@stdlib/random/iter/uniform' );
var itermprod = require( '@stdlib/stats/iter/mprod' );

// Create an iterator for generating uniformly distributed pseudorandom numbers:
var rand = runif( -10.0, 10.0, {
    'seed': 1234,
    'iter': 100
});

// Create an iterator for iteratively computing a moving product:
var it = itermprod( rand, 3 );

// Perform manual iteration...
var v;
while ( true ) {
    v = it.next();
    if ( typeof v.value === 'number' ) {
        console.log( 'product: %d', v.value );
    }
    if ( v.done ) {
        break;
    }
}