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# ind2sub

> Convert a linear index to an array of subscripts.

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## Usage

```javascript
var ind2sub = require( '@stdlib/ndarray/ind2sub' );
```

#### ind2sub( shape, idx\[, options] )

Converts a linear index to an array of subscripts.

```javascript
var shape = [ 2, 2 ];

var s = ind2sub( shape, 2 );
// returns [ 1, 0 ]
```

The function supports the following `options`:

-   **mode**: specifies how to handle a linear index which exceeds array dimensions. The following modes are supported:

    -   `throw`: specifies that the function should throw an error when a linear index exceeds array dimensions.
    -   `normalize`: specifies that the function should normalize negative linear indices and 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.

-   **order**: specifies whether an array is `row-major` (C-style) or `column-major` (Fortran-style). Default: `'row-major'`.

By default, the function assumes a row-major array. To return subscripts for a column-major array, set the `order` option.

```javascript
var shape = [ 2, 2 ];
var opts = {};

opts.order = 'column-major';
var s = ind2sub( shape, 1, opts );
// returns [ 1, 0 ]
```

By default, the function throws an `error` if provided a linear index which exceeds array dimensions. To specify alternative behavior, set the `mode` option.

```javascript
var shape = [ 2, 2 ];
var opts = {};

opts.mode = 'wrap';
var s = ind2sub( shape, -5, opts );
// returns [ 1, 1 ]

opts.mode = 'clamp';
s = ind2sub( shape, 7, opts );
// returns [ 1, 1 ]
```

#### ind2sub.assign( shape, idx\[, options], out )

Converts a linear index to an array of subscripts and assigns results to a provided output array.

```javascript
var shape = [ 2, 2 ];
var out = [ 0, 0 ];

var subscripts = ind2sub.assign( shape, 1, out );
// returns [ 0, 1 ]

var bool = ( subscripts === out );
// returns true
```

The function accepts the same `options` as above.

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## Examples

<!-- eslint no-undef: "error" -->

```javascript
var numel = require( '@stdlib/ndarray/base/numel' );
var ind2sub = require( '@stdlib/ndarray/ind2sub' );

var shape = [ 3, 3, 3 ];
var len = numel( shape );

var arr = [];
var i;
for ( i = 0; i < len; i++ ) {
    arr.push( i );
}

var opts = {
    'order': 'column-major'
};

console.log( '' );
console.log( 'Dimensions: %s.', shape.join( 'x' ) );
console.log( 'View (subscripts):' );
console.log( '' );

var row;
var s;

row = '  ';
for ( i = 0; i < len; i++ ) {
    s = ind2sub( shape, i, opts );
    row += '(' + s.join( ',' ) + ')';
    if ( (i+1)%shape[0] === 0 ) {
        console.log( row );
        row = '  ';
    } else {
        row += ', ';
    }
    if ( (i+1)%(shape[0]*shape[1]) === 0 ) {
        console.log( '' );
    }
}
```

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* * *

## See Also

-   <span class="package-name">[`@stdlib/ndarray/array`][@stdlib/ndarray/array]</span><span class="delimiter">: </span><span class="description">multidimensional arrays.</span>
-   <span class="package-name">[`@stdlib/ndarray/ctor`][@stdlib/ndarray/ctor]</span><span class="delimiter">: </span><span class="description">multidimensional array constructor.</span>
-   <span class="package-name">[`@stdlib/ndarray/sub2ind`][@stdlib/ndarray/sub2ind]</span><span class="delimiter">: </span><span class="description">convert subscripts to a linear index.</span>

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[@stdlib/ndarray/array]: https://github.com/stdlib-js/ndarray/tree/main/array

[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/ndarray/tree/main/ctor

[@stdlib/ndarray/sub2ind]: https://github.com/stdlib-js/ndarray/tree/main/sub2ind

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