time-to-botec

README.md (6211B)

---

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 # sub2ind
 
 > Convert subscripts to a linear index.
 
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 <!-- Package usage documentation. -->
 
 <section class="usage">
 
 ## Usage
 
 ```javascript
 var sub2ind = require( '@stdlib/ndarray/base/sub2ind' );
 ```
 
 #### sub2ind( shape, strides, offset, ...subscripts, mode )
 
 Converts subscripts to a linear index.
 
 ```javascript
 var shape = [ 2, 2 ];
 var strides = [ 2, 1 ];
 var offset = 0;
 var mode = [ 'throw' ];
 
 var idx = sub2ind( shape, strides, offset, 1, 0, mode );
 // returns 2
 ```
 
 The function supports the following `modes`:
 
 -   `throw`: specifies that the function should throw an error when a subscript exceeds array dimensions.
 -   `wrap`: specifies that the function should wrap around subscripts exceeding array dimensions using modulo arithmetic.
 -   `clamp`: specifies that the function should set subscripts exceeding array dimensions to either `0` (minimum index) or the maximum index along a particular dimension.
 
 ```javascript
 var shape = [ 2, 2 ];
 var strides = [ 2, 1 ];
 var offset = 0;
 
 var mode = [ 'wrap' ];
 var idx = sub2ind( shape, strides, offset, -2, 0, mode );
 // returns 0
 
 mode = [ 'clamp' ];
 idx = sub2ind( shape, strides, offset, 10, 10, mode );
 // returns 3
 ```
 
 </section>
 
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 ## Notes
 
 -   When provided fewer `modes` than dimensions, the function recycles `modes` using modulo arithmetic.
 
     ```javascript
     var shape = [ 2, 2, 2 ];
     var strides = [ 4, 2, 1 ];
     var offset = 0;
     var mode = [ 'wrap', 'clamp' ];
 
     var idx = sub2ind( shape, strides, offset, -2, 10, -1, mode );
     // returns 3
     ```
 
 -   When provided a stride array containing negative strides, if an `offset` is greater than `0`, the function treats subscripts as mapping to a linear index in an underlying data buffer for the array, thus returning a linear index from the perspective of that buffer. If an `offset` is equal to `0`, the function treats subscripts as mapping to a linear index in an array view, thus returning a linear index from the perspective of that view.
 
     ```text
     Dims: 2x2
     Buffer: [ 1, 2, 3, 4 ]
 
     View = [ a00, a01,
              a10, a11 ]
 
     Strides: 2,1
     Offset: 0
 
     View = [ 1, 2,
              3, 4 ]
 
     Strides: 2,-1
     Offset: 1
 
     View = [ 2, 1,
              4, 3 ]
 
     Strides: -2,1
     Offset: 2
 
     View = [ 3, 4,
              1, 2 ]
 
     Strides: -2,-1
     Offset: 3
 
     View = [ 4, 3,
              2, 1 ]
     ```
 
     ```javascript
     var shape = [ 2, 2 ];
     var strides = [ -2, 1 ];
     var offset = 2;
     var mode = [ 'throw' ];
 
     // From the perspective of a view...
     var idx = sub2ind( shape, strides, 0, 0, 0, mode );
     // returns 0
 
     idx = sub2ind( shape, strides, 0, 0, 1, mode );
     // returns 1
 
     idx = sub2ind( shape, strides, 0, 1, 0, mode );
     // returns 2
 
     idx = sub2ind( shape, strides, 0, 1, 1, mode );
     // returns 3
 
     // From the perspective of an underlying buffer...
     idx = sub2ind( shape, strides, offset, 0, 0, mode );
     // returns 2
 
     idx = sub2ind( shape, strides, offset, 0, 1, mode );
     // returns 3
 
     idx = sub2ind( shape, strides, offset, 1, 0, mode );
     // returns 0
 
     idx = sub2ind( shape, strides, offset, 1, 1, mode );
     // returns 1
     ```
 
     In short, from the perspective of a view, view data is always ordered.
 
 </section>
 
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 ## Examples
 
 <!-- eslint no-undef: "error" -->
 
 ```javascript
 var discreteUniform = require( '@stdlib/random/base/discrete-uniform' );
 var shape2strides = require( '@stdlib/ndarray/base/shape2strides' );
 var strides2offset = require( '@stdlib/ndarray/base/strides2offset' );
 var numel = require( '@stdlib/ndarray/base/numel' );
 var randu = require( '@stdlib/random/base/randu' );
 var sub2ind = require( '@stdlib/ndarray/base/sub2ind' );
 
 var shape = [ 3, 3 ];
 var strides = shape2strides( shape, 'row-major' );
 var mode = [ 'throw' ];
 var len = numel( shape );
 
 var arr = [];
 var i;
 for ( i = 0; i < len; i++ ) {
     arr.push( i );
 }
 
 var offset;
 var idx;
 var row;
 var j;
 var n;
 var m;
 for ( i = 0; i < 20; i++ ) {
     j = discreteUniform( 0, shape.length-1 );
     strides[ j ] = ( randu() < 0.5 ) ? -1 : 1;
     offset = strides2offset( shape, strides );
 
     console.log( '' );
     console.log( 'Dimensions: %s.', shape.join( 'x' ) );
     console.log( 'Strides: %s.', strides.join( ',' ) );
     console.log( 'View:' );
     for ( n = 0; n < shape[ 0 ]; n++ ) {
         row = '  ';
         for ( m = 0; m < shape[ 1 ]; m++ ) {
             idx = sub2ind( shape, strides, offset, n, m, mode );
             row += arr[ idx ];
             if ( m < shape[ 1 ]-1 ) {
                 row += ', ';
             }
         }
         console.log( row );
     }
 }
 ```
 
 </section>
 
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