time-to-botec

README.md (10630B)

---

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 # ind2sub
 
 > Convert a linear index to an array of subscripts.
 
 <!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
 
 <section class="intro">
 
 </section>
 
 <!-- /.intro -->
 
 <!-- Package usage documentation. -->
 
 <section class="usage">
 
 ## Usage
 
 ```javascript
 var ind2sub = require( '@stdlib/ndarray/base/ind2sub' );
 ```
 
 #### ind2sub( shape, strides, offset, order, idx, mode )
 
 Converts a linear index to an array of subscripts.
 
 ```javascript
 var shape = [ 2, 2 ];
 var order = 'row-major';
 var strides = [ 2, 1 ];
 var offset = 0;
 
 var subscripts = ind2sub( shape, strides, offset, order, 1, 'throw' );
 // returns [ 0, 1 ]
 ```
 
 The function supports the following `modes`:
 
 -   `throw`: specifies that the function should throw an error when a linear index exceeds array dimensions.
 -   `wrap`: specifies that the function should wrap around a linear index exceeding array dimensions using modulo arithmetic.
 -   `clamp`: specifies that the function should set a linear index exceeding array dimensions to either `0` (minimum linear index) or the maximum linear index.
 
 ```javascript
 var shape = [ 2, 2 ];
 var order = 'row-major';
 var strides = [ 2, 1 ];
 var offset = 0;
 
 var idx = ind2sub( shape, strides, offset, order, -2, 'wrap' );
 // returns [ 1, 0 ]
 
 idx = ind2sub( shape, strides, offset, order, 10, 'clamp' );
 // returns [ 1, 1 ]
 ```
 
 The `order` parameter specifies whether an array is `row-major` (C-style) or `column-major` (Fortran-style).
 
 ```javascript
 var shape = [ 2, 2 ];
 var order = 'column-major';
 var strides = [ 1, 2 ];
 var offset = 0;
 
 var idx = ind2sub( shape, strides, offset, order, 2, 'throw' );
 // returns [ 0, 1 ]
 ```
 
 #### ind2sub.assign( shape, strides, offset, order, idx, mode, out )
 
 Converts a linear index to an array of subscripts and assigns results to a provided output array.
 
 ```javascript
 var shape = [ 2, 2 ];
 var order = 'row-major';
 var strides = [ 2, 1 ];
 var offset = 0;
 
 var out = [ 0, 0 ];
 var subscripts = ind2sub.assign( shape, strides, offset, order, 1, 'throw', out );
 // returns [ 0, 1 ]
 
 var bool = ( subscripts === out );
 // returns true
 ```
 
 </section>
 
 <!-- /.usage -->
 
 <!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
 
 <section class="notes">
 
 ## Notes
 
 -   When provided a stride array containing negative strides, if an `offset` is greater than `0`, the function interprets the linear index as an index into the underlying data buffer for the array, thus returning subscripts from the perspective of that buffer. If an `offset` is equal to `0`, the function treats the linear index as an index into an array view, thus returning subscripts 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 order = 'row-major';
     var strides = [ -2, 1 ];
     var offset = 2;
     var mode = 'throw';
 
     // From the perspective of a view...
     var s = ind2sub( shape, strides, 0, order, 0, mode );
     // returns [ 0, 0 ]
 
     s = ind2sub( shape, strides, 0, order, 1, mode );
     // returns [ 0, 1 ]
 
     s = ind2sub( shape, strides, 0, order, 2, mode );
     // returns [ 1, 0 ]
 
     s = ind2sub( shape, strides, 0, order, 3, mode );
     // returns [ 1, 1 ]
 
     // From the perspective of an underlying buffer...
     s = ind2sub( shape, strides, offset, order, 0, mode );
     // returns [ 1, 0 ]
 
     s = ind2sub( shape, strides, offset, order, 1, mode );
     // returns [ 1, 1 ]
 
     s = ind2sub( shape, strides, offset, order, 2, mode );
     // returns [ 0, 0 ]
 
     s = ind2sub( shape, strides, offset, order, 3, mode );
     // returns [ 0, 1 ]
     ```
 
     In short, from the perspective of a view, view data is always ordered.
 
 </section>
 
 <!-- /.notes -->
 
 <!-- Package usage examples. -->
 
 <section class="examples">
 
 ## 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 abs = require( '@stdlib/math/base/special/abs' );
 var ind2sub = require( '@stdlib/ndarray/base/ind2sub' );
 
 // Specify array characteristics:
 var shape = [ 3, 3, 3 ];
 var order = 'row-major';
 
 // Compute array meta data:
 var ndims = shape.length;
 var strides = shape2strides( shape, order );
 var len = numel( shape );
 
 // Determine stride indices to be used for formatting how views are displayed...
 var s0;
 var s1;
 if ( order === 'column-major' ) {
     s0 = ndims - 1;
     s1 = s0 - 1;
 } else { // row-major
     s0 = 0;
     s1 = s0 + 1;
 }
 
 // Initialize a linear array...
 var arr = [];
 var i;
 for ( i = 0; i < len; i++ ) {
     arr.push( 0 );
 }
 
 // Generate random views and display the mapping of elements in the linear array to view subscripts...
 var offset;
 var row;
 var j;
 var s;
 for ( i = 0; i < 20; i++ ) {
     // Randomly flip the sign of one of the strides...
     j = discreteUniform( 0, ndims-1 );
     strides[ j ] *= ( randu() < 0.5 ) ? -1 : 1;
     offset = strides2offset( shape, strides );
 
     // Print view meta data...
     console.log( '' );
     console.log( 'Dimensions: %s.', shape.join( 'x' ) );
     console.log( 'Strides: %s.', strides.join( ',' ) );
     console.log( 'View (subscripts):' );
 
     // Print the mapping of elements in the linear array to view subscripts...
     row = '  ';
     for ( j = 0; j < len; j++ ) {
         s = ind2sub( shape, strides, offset, order, j, 'throw' );
         row += '(' + s.join( ',' ) + ')';
         if ( ndims === 1 && j === len-1 ) {
             console.log( row );
         } else if ( ndims === 2 && (j+1)%abs( strides[ s0 ] ) === 0 ) {
             console.log( row );
             row = '  ';
         } else if ( ndims > 2 && (j+1)%abs( strides[ s1 ] ) === 0 ) {
             console.log( row );
             if ( (j+1)%abs( strides[ s0 ] ) === 0 ) {
                 console.log( '' );
             }
             row = '  ';
         } else {
             row += ', ';
         }
     }
 }
 ```
 
 </section>
 
 <!-- /.examples -->
 
 <!-- C interface documentation. -->
 
 * * *
 
 <section class="c">
 
 ## C APIs
 
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 <section class="intro">
 
 </section>
 
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 <!-- C usage documentation. -->
 
 <section class="usage">
 
 ### Usage
 
 ```c
 #include "stdlib/ndarray/base/ind2sub.h"
 ```
 
 <!-- lint disable maximum-heading-length -->
 
 #### stdlib_ndarray_ind2sub( ndims, \*shape, \*strides, offset, order, idx, mode, \*out )
 
 Computes the minimum and maximum linear indices in an underlying data buffer accessible to an array view.
 
 ```c
 #include "stdlib/ndarray/index_modes.h"
 #include "stdlib/ndarray/orders.h"
 #include <stdint.h>
 
 int64_t ndims = 2;
 int64_t shape[] = { 3, 3 };
 int64_t strides[] = { -3, 1 };
 int64_t offset = 6;
 
 int64_t out[ 2 ];
 
 int8_t status = stdlib_ndarray_ind2sub( ndims, shape, strides, offset, STDLIB_NDARRAY_ROW_MAJOR, 7, STDLIB_NDARRAY_INDEX_ERROR, out );
 if ( status == -1 ) {
     // Handle error...
 }
 ```
 
 The function accepts the following arguments:
 
 -   **ndims**: `[in] int64_t` number of dimensions.
 -   **shape**: `[in] int64_t*` array shape (dimensions).
 -   **strides**: `[in] int64_t*` array strides.
 -   **offset**: `[in] int64_t` index offset.
 -   **order**: `[in] enum STDLIB_NDARRAY_ORDER` specifies whether an array is row-major (C-style) or column-major (Fortran-style).
 -   **idx**: `[in] int64_t` linear index in an array view.
 -   **mode**: `[in] enum STDLIB_NDARRAY_INDEX_MODE` specifies how to handle a linear index which exceeds array dimensions.
 -   **out**: `[out] int64_t*` output array.
 
 ```c
 int8_t stdlib_ndarray_ind2sub( int64_t ndims, int64_t *shape, int64_t *strides, int64_t offset, enum STDLIB_NDARRAY_ORDER order, int64_t idx, enum STDLIB_NDARRAY_INDEX_MODE mode, int64_t *out );
 ```
 
 </section>
 
 <!-- /.usage -->
 
 <!-- C API usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
 
 <section class="notes">
 
 </section>
 
 <!-- /.notes -->
 
 <!-- C API usage examples. -->
 
 <section class="examples">
 
 ### Examples
 
 ```c
 #include "stdlib/ndarray/base/ind2sub.h"
 #include "stdlib/ndarray/index_modes.h"
 #include "stdlib/ndarray/orders.h"
 #include <stdint.h>
 #include <stdio.h>
 #include <inttypes.h>
 
 int main() {
     int64_t ndims = 2;
     int64_t shape[] = { 3, 3 };
     int64_t strides[] = { -3, 1 };
     int64_t offset = 6;
 
     int64_t out[ 2 ];
 
     stdlib_ndarray_ind2sub( ndims, shape, strides, offset, STDLIB_NDARRAY_ROW_MAJOR, 7, STDLIB_NDARRAY_INDEX_ERROR, out );
 
     int i;
     printf( "subscripts = { " );
     for ( i = 0; i < ndims; i++ ) {
         printf( "%"PRId64"", out[ i ] );
         if ( i < ndims-1 ) {
             printf( ", " );
         }
     }
     printf( " }\n" );
 }
 ```
 
 </section>
 
 <!-- /.examples -->
 
 </section>
 
 <!-- /.c -->
 
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