time-to-botec

README.md (5935B)

---

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 # rangeBy
 
 > Calculate the [range][range] of a strided array via a callback function.
 
 <section class="intro">
 
 The [**range**][range] is defined as the difference between the maximum and minimum values.
 
 </section>
 
 <!-- /.intro -->
 
 <section class="usage">
 
 ## Usage
 
 ```javascript
 var rangeBy = require( '@stdlib/stats/base/range-by' );
 ```
 
 #### rangeBy( N, x, stride, clbk\[, thisArg] )
 
 Calculates the [range][range] of strided array `x` via a callback function.
 
 ```javascript
 function accessor( v ) {
     return v * 2.0;
 }
 
 var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
 
 var v = rangeBy( x.length, x, 1, accessor );
 // returns 18.0
 ```
 
 The function has the following parameters:
 
 -   **N**: number of indexed elements.
 -   **x**: input [`Array`][mdn-array], [`typed array`][mdn-typed-array], or an array-like object (excluding strings and functions). 
 -   **stride**: index increment.
 -   **clbk**: callback function.
 -   **thisArg**: execution context (_optional_).
 
 The invoked callback is provided four arguments:
 
 -   **value**: array element.
 -   **aidx**: array index.
 -   **sidx**: strided index (`offset + aidx*stride`).
 -   **array**: input array/collection.
 
 To set the callback execution context, provide a `thisArg`.
 
 ```javascript
 function accessor( v ) {
     this.count += 1;
     return v * 2.0;
 }
 
 var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
 
 var context = {
     'count': 0
 };
 
 var v = rangeBy( x.length, x, 1, accessor, context );
 // returns 18.0
 
 var cnt = context.count;
 // returns 8
 ```
 
 The `N` and `stride` parameters determine which elements in `x` are accessed at runtime. For example, to access every other element
 
 ```javascript
 var floor = require( '@stdlib/math/base/special/floor' );
 
 function accessor( v ) {
     return v * 2.0;
 }
 
 var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
 var N = floor( x.length / 2 );
 
 var v = rangeBy( N, x, 2, accessor );
 // returns 12.0
 ```
 
 Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
 
 ```javascript
 var Float64Array = require( '@stdlib/array/float64' );
 var floor = require( '@stdlib/math/base/special/floor' );
 
 function accessor( v ) {
     return v * 2.0;
 }
 
 // Initial array...
 var x0 = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
 
 // Create an offset view...
 var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
 var N = floor( x0.length/2 );
 
 // Access every other element...
 var v = rangeBy( N, x1, 2, accessor );
 // returns 8.0
 ```
 
 #### rangeBy.ndarray( N, x, stride, offset, clbk\[, thisArg] )
 
 Calculates the [range][range] of strided array `x` via a callback function and using alternative indexing semantics.
 
 ```javascript
 function accessor( v ) {
     return v * 2.0;
 }
 
 var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
 
 var v = rangeBy.ndarray( x.length, x, 1, 0, accessor );
 // returns 18.0
 ```
 
 The function has the following additional parameters:
 
 -   **offset**: starting index.
 
 While [`typed array`][mdn-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 access only the last three elements of `x`
 
 ```javascript
 function accessor( v ) {
     return v * 2.0;
 }
 
 var x = [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ];
 
 var v = rangeBy.ndarray( 3, x, 1, x.length-3, accessor );
 // returns 22.0
 ```
 
 </section>
 
 <!-- /.usage -->
 
 <section class="notes">
 
 ## Notes
 
 -   If `N <= 0`, both functions return `NaN`.
 -   A provided callback function should return a numeric value.
 -   If a provided callback function does not return any value (or equivalently, explicitly returns `undefined`), the value is **ignored**.
 -   When possible, prefer using [`drange`][@stdlib/stats/base/drange], [`srange`][@stdlib/stats/base/srange], and/or [`range`][@stdlib/stats/base/range], as, depending on the environment, these interfaces are likely to be significantly more performant.
 
 </section>
 
 <!-- /.notes -->
 
 <section class="examples">
 
 ## Examples
 
 <!-- eslint no-undef: "error" -->
 
 ```javascript
 var round = require( '@stdlib/math/base/special/round' );
 var randu = require( '@stdlib/random/base/randu' );
 var Float64Array = require( '@stdlib/array/float64' );
 var gfillBy = require( '@stdlib/blas/ext/base/gfill-by' );
 var rangeBy = require( '@stdlib/stats/base/range-by' );
 
 function fill() {
     return round( ( randu()*100.0 ) - 50.0 );
 }
 
 function accessor( v ) {
     return v * 2.0;
 }
 
 var x = new Float64Array( 10 );
 
 gfillBy( x.length, x, 1, fill );
 console.log( x );
 
 var v = rangeBy( x.length, x, 1, accessor );
 console.log( v );
 ```
 
 </section>
 
 <!-- /.examples -->
 
 <section class="links">
 
 [range]: https://en.wikipedia.org/wiki/Range_%28statistics%29
 
 [mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
 
 [mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
 
 [@stdlib/stats/base/drange]: https://www.npmjs.com/package/@stdlib/stats/tree/main/base/drange
 
 [@stdlib/stats/base/range]: https://www.npmjs.com/package/@stdlib/stats/tree/main/base/range
 
 [@stdlib/stats/base/srange]: https://www.npmjs.com/package/@stdlib/stats/tree/main/base/srange
 
 </section>
 
 <!-- /.links -->