# ind
> Return an index given an index mode.
## Usage
```javascript
var ind = require( '@stdlib/ndarray/base/ind' );
```
#### ind( idx, max, mode )
Returns an index given an index `mode`.
```javascript
var idx = ind( 2, 9, 'throw' );
// returns 2
idx = ind( -1, 9, 'throw' );
// throws
idx = ind( 10, 9, 'throw' );
// throws
// Wrapping indices around using modulo arithmetic:
idx = ind( 2, 9, 'wrap' );
// returns 2
idx = ind( 10, 9, 'wrap' );
// returns 0
idx = ind( -1, 9, 'wrap' );
// returns 9
// Clamping indices to first and last indices:
idx = ind( 2, 9, 'clamp' );
// returns 2
idx = ind( 10, 9, 'clamp' );
// returns 9
idx = ind( -1, 9, 'clamp' );
// returns 0
// Normalizing negative indices:
idx = ind( 2, 9, 'normalize' );
// returns 2
idx = ind( -4, 9, 'normalize' );
// returns 6
```
#### ind.factory( mode )
Returns a function for returning an index according to a provided index `mode`.
```javascript
var fcn = ind.factory( 'clamp' );
var idx = fcn( 2, 9 );
// returns 2
idx = fcn( 10, 9 );
// returns 9
idx = fcn( -1, 9 );
// returns 0
```
The function returns a function accepts the following arguments:
- **index**: input index.
- **max**: maximum index value.
## Notes
- Both functions support the following modes:
- **throw**: specifies that the function should throw an error when an index is outside the interval `[0, max]`.
- **normalize**: specifies that the function should normalize negative indices and throw an error when an index is outside the interval `[-max-1, max]`.
- **wrap**: specifies that the function should wrap around an index using modulo arithmetic.
- **clamp**: specifies that the function should set an index less than `0` to `0` (minimum index) and set an index greater than `max` to `max`.
## Examples
```javascript
var discreteUniform = require( '@stdlib/random/base/discrete-uniform' );
var ind = require( '@stdlib/ndarray/base/ind' );
var modes;
var mode;
var idx;
var out;
var i;
modes = [ 'clamp', 'wrap' ];
for ( i = 0; i < 100; i++ ) {
idx = discreteUniform( -20, 20 );
mode = modes[ discreteUniform( 0, modes.length-1 ) ];
out = ind( idx, 9, mode );
console.log( '%d => %s(%d,%d) => %d', idx, mode, 0, 9, out );
}
```