time-to-botec

README.md (7203B)

---

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 # Dispatch
 
 > Create an [ndarray][@stdlib/ndarray/ctor] function interface which performs multiple dispatch.
 
 <section class="intro">
 
 </section>
 
 <!-- /.intro -->
 
 <section class="usage">
 
 ## Usage
 
 ```javascript
 var dispatch = require( '@stdlib/ndarray/dispatch' );
 ```
 
 #### dispatch( fcns, types, data, nargs, nin, nout )
 
 Returns an [ndarray][@stdlib/ndarray/ctor] function interface which performs multiple dispatch.
 
 <!-- eslint-disable array-element-newline -->
 
 ```javascript
 var unary = require( '@stdlib/ndarray/base/unary' );
 var Float64Array = require( '@stdlib/array/float64' );
 var Float32Array = require( '@stdlib/array/float32' );
 var ndarray = require( '@stdlib/ndarray/ctor' );
 
 function foo( x ) {
     return x * 10.0;
 }
 
 function bar( x ) {
     return x * 5.0;
 }
 
 // Define a list of ndarray functions for applying a unary callback:
 var fcns = [
     unary,
     unary
 ];
 
 // Define a one-dimensional list of input and output array types:
 var types = [
     'float64', 'float64', // input, output
     'float32', 'float32'  // input, output
 ];
 
 // Define a list of callbacks which should be applied based on the provided array types:
 var data = [
     foo,
     bar
 ];
 
 // Define the total number of input arguments:
 var nargs = 2; // input_array + output_array
 
 // Define the number of input ndarrays:
 var nin = 1;
 
 // Define the number of output ndarrays:
 var nout = 1;
 
 // Create an ndarray function interface:
 var fcn = dispatch( fcns, types, data, nargs, nin, nout );
 
 // ...
 
 var xbuf = new Float64Array( [ 1.0, 2.0, 3.0 ] );
 var ybuf = new Float64Array( xbuf.length );
 
 var x = ndarray( 'float64', xbuf, [ 3 ], [ 1 ], 0, 'row-major' );
 var y = ndarray( 'float64', ybuf, [ 3 ], [ 1 ], 0, 'row-major' );
 
 fcn( x, y );
 // ybuf => <Float64Array>[ 10.0, 20.0, 30.0 ]
 
 xbuf = new Float32Array( [ 1.0, 2.0, 3.0 ] );
 ybuf = new Float32Array( xbuf.length );
 
 x = ndarray( 'float32', xbuf, [ 3 ], [ 1 ], 0, 'row-major' );
 y = ndarray( 'float32', ybuf, [ 3 ], [ 1 ], 0, 'row-major' );
 
 fcn( x, y );
 // ybuf => <Float32Array>[ 5.0, 10.0, 15.0 ]
 ```
 
 The function accepts the following arguments:
 
 -   **fcns**: list of [ndarray][@stdlib/ndarray/ctor] functions.
 -   **types**: one-dimensional list of [ndarray][@stdlib/ndarray/ctor] argument data types. The length of `types` must be the number of [ndarray][@stdlib/ndarray/ctor] functions multiplied by `nin+nout`. If `fcns` is a function, rather than a list, the number of [ndarray][@stdlib/ndarray/ctor] functions is computed as `types.length / (nin+nout)`.
 -   **data**: [ndarray][@stdlib/ndarray/ctor] function data (e.g., callbacks). If a list, the length of `data` must equal the number of [ndarray][@stdlib/ndarray/ctor] functions. If `null`, a returned [ndarray][@stdlib/ndarray/ctor] function interface does **not** provide a `data` argument to an invoked [ndarray][@stdlib/ndarray/ctor] function.
 -   **nargs**: total number of [ndarray][@stdlib/ndarray/ctor] function interface arguments.
 -   **nin**: number of input [ndarrays][@stdlib/ndarray/ctor].
 -   **nout**: number of output [ndarrays][@stdlib/ndarray/ctor].
 
 </section>
 
 <!-- /.usage -->
 
 <section class="notes">
 
 ## Notes
 
 -   A returned [ndarray][@stdlib/ndarray/ctor] function interface has the following signature:
 
     ```text
     f( x, y, ... )
     ```
 
     where
 
     -   **x**: [ndarray][@stdlib/ndarray/ctor].
     -   **y**: [ndarray][@stdlib/ndarray/ctor].
     -   **...**: additional [ndarrays][@stdlib/ndarray/ctor].
 
 -   The number of [ndarray][@stdlib/ndarray/ctor] function interface parameters is derived from `nargs`, the number of input [ndarrays][@stdlib/ndarray/ctor] is derived from `nin`, and the number of output [ndarrays][@stdlib/ndarray/ctor] is derived from `nout`.
 
 -   An [ndarray][@stdlib/ndarray/ctor] function (i.e., a value provided for the `fcns` argument) should have the following signature:
 
     ```text
     f( arrays[, data] )
     ```
 
     where
 
     -   **arrays**: array containing input and output [ndarrays][@stdlib/ndarray/ctor].
     -   **data**: [ndarray][@stdlib/ndarray/ctor] function data (e.g., a callback).
 
 -   For convenience, a single [ndarray][@stdlib/ndarray/ctor] function may be provided which will be invoked whenever the [ndarray][@stdlib/ndarray/ctor] argument data types match a sequence of types in `types`. Providing a single [ndarray][@stdlib/ndarray/ctor] function is particularly convenient for the case where, regardless of array data types, traversing arrays remains the same, but the [ndarray][@stdlib/ndarray/ctor] function `data` differs (e.g., callbacks which differ based on the array data types). For example, the following
 
     <!-- eslint-disable array-element-newline -->
 
     ```javascript
     var unary = require( '@stdlib/ndarray/base/unary' );
 
     function foo( x ) {
         return x * 10.0;
     }
 
     function bar( x ) {
         return x * 5.0;
     }
 
     var fcns = [
         unary,
         unary
     ];
     var types = [
         'float64', 'float64',
         'float32', 'float32'
     ];
     var data = [
         foo,
         bar
     ];
 
     var fcn = dispatch( fcns, types, data, 2, 1, 1 );
     ```
 
     is equivalent to
 
     <!-- eslint-disable array-element-newline -->
 
     ```javascript
     var unary = require( '@stdlib/ndarray/base/unary' );
 
     function foo( x ) {
         return x * 10.0;
     }
 
     function bar( x ) {
         return x * 5.0;
     }
 
     var types = [
         'float64', 'float64',
         'float32', 'float32'
     ];
     var data = [
         foo,
         bar
     ];
 
     var fcn = dispatch( unary, types, data, 2, 1, 1 );
     ```
 
 </section>
 
 <!-- /.notes -->
 
 <section class="examples">
 
 ## Examples
 
 <!-- eslint no-undef: "error" -->
 
 ```javascript
 var unary = require( '@stdlib/ndarray/base/unary' );
 var ndarray = require( '@stdlib/ndarray/ctor' );
 var abs = require( '@stdlib/math/base/special/abs' );
 var Float64Array = require( '@stdlib/array/float64' );
 var dispatch = require( '@stdlib/ndarray/dispatch' );
 
 var types = [ 'float64', 'float64' ];
 
 var data = [
     abs
 ];
 
 var absolute = dispatch( unary, types, data, 2, 1, 1 );
 
 var xbuf = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0 ] );
 var ybuf = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0 ] );
 
 var x = ndarray( 'float64', xbuf, [ 5 ], [ 1 ], 0, 'row-major' );
 var y = ndarray( 'float64', ybuf, [ 5 ], [ 1 ], 0, 'row-major' );
 
 absolute( x, y );
 console.log( ybuf );
 // => <Float64Array>[ 1.0, 2.0, 3.0, 4.0, 5.0 ]
 ```
 
 </section>
 
 <!-- /.examples -->
 
 <section class="links">
 
 [@stdlib/ndarray/ctor]: https://www.npmjs.com/package/@stdlib/ndarray/tree/main/ctor
 
 </section>
 
 <!-- /.links -->