# sub2ind
> Convert subscripts to a linear index.
## Usage
```javascript
var sub2ind = require( '@stdlib/ndarray/sub2ind' );
```
#### sub2ind( shape, ...subscripts\[, options] )
Converts subscripts to a linear index.
```javascript
var shape = [ 2, 2 ];
var idx = sub2ind( shape, 1, 0 );
// returns 2
```
The function supports the following `options`:
- `mode`: specifies how to handle subscripts which exceed array dimensions. The following modes are supported:
- `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.
If provided a `mode` array, each array element corresponds to a dimension. If provided fewer modes than dimensions, the function reuses modes using modulo arithmetic. Default: `[ 'throw' ]`.
- `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 a linear index for a column-major array, set the `order` option.
```javascript
var shape = [ 2, 2 ];
var opts = {};
opts.order = 'column-major';
var idx = sub2ind( shape, 1, 0, opts );
// returns 1
```
By default, the function throws an `error` if provided subscripts which exceed array dimensions. To specify alternative behavior, set the `mode` option.
```javascript
var shape = [ 2, 2 ];
var opts = {};
opts.mode = 'wrap';
var idx = sub2ind( shape, -2, 0, opts );
// returns 0
opts.mode = 'clamp';
idx = sub2ind( shape, 10, 10, opts );
// returns 3
```
To specify separate modes for each dimension, provide a `mode` array.
```javascript
var shape = [ 2, 2, 2 ];
var opts = {
'mode': [
'wrap',
'clamp'
]
};
var idx = sub2ind( shape, -2, 10, -1, opts );
// returns 3
```
## Examples
```javascript
var numel = require( '@stdlib/ndarray/base/numel' );
var sub2ind = require( '@stdlib/ndarray/sub2ind' );
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:' );
console.log( '' );
var slice;
var idx;
var row;
var j;
var k;
for ( k = 0; k < shape[ 2 ]; k++ ) {
slice = 'A[:,:,'+k+'] = ';
console.log( slice );
for ( i = 0; i < shape[ 0 ]; i++ ) {
row = ' ';
for ( j = 0; j < shape[ 1 ]; j++ ) {
idx = sub2ind( shape, i, j, k, opts );
row += arr[ idx ];
if ( j < shape[ 1 ]-1 ) {
row += ', ';
}
}
console.log( row );
}
console.log( '' );
}
```