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# join

> Return an [ndarray][@stdlib/ndarray/ctor] created by joining elements using a separator along one or more [ndarray][@stdlib/ndarray/ctor] dimensions.

<section class="usage">

## Usage

```javascript
var join = require( '@stdlib/blas/ext/join' );
```

#### join( x\[, options] )

Returns an [ndarray][@stdlib/ndarray/ctor] created by joining elements using a separator along one or more [ndarray][@stdlib/ndarray/ctor] dimensions.

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

// Create an input ndarray:
var x = array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
// returns <ndarray>

// Perform operation:
var out = join( x );
// returns <ndarray>[ '1,2,3,4,5,6' ]
```

The function has the following parameters:

-   **x**: input [ndarray][@stdlib/ndarray/ctor].
-   **options**: function options (_optional_).

The function accepts the following options:

-   **sep**: separator. May be either a scalar value or an [ndarray][@stdlib/ndarray/ctor] having a "generic" [data type][@stdlib/ndarray/dtypes]. If provided an [ndarray][@stdlib/ndarray/ctor], the value must have a shape which is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with the complement of the shape defined by `options.dims`. For example, given the input shape `[2, 3, 4]` and `options.dims=[0]`, an [ndarray][@stdlib/ndarray/ctor] separator value must have a shape which is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with the shape `[3, 4]`. Similarly, when performing the operation over all elements in a provided input [ndarray][@stdlib/ndarray/ctor], an [ndarray][@stdlib/ndarray/ctor] separator value must be a zero-dimensional [ndarray][@stdlib/ndarray/ctor]. Default: `,`.
-   **dims**: list of dimensions over which to perform operation. If not provided, the function performs the operation over all elements in a provided input [ndarray][@stdlib/ndarray/ctor].
-   **keepdims**: boolean indicating whether the reduced dimensions should be included in the returned [ndarray][@stdlib/ndarray/ctor] as singleton dimensions. Default: `false`.

By default, the function joins [ndarray][@stdlib/ndarray/ctor] elements by using `,` as a separator. To perform the operation with a different separator, provide a `sep` option.

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

var x = array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );

var out = join( x, {
    'sep': '|'
});
// returns <ndarray>[ '1|2|3|4|5|6' ]
```

By default, the function performs the operation over all elements in a provided input [ndarray][@stdlib/ndarray/ctor]. To perform the operation over specific dimensions, provide a `dims` option.

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

var x = array( [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ] );

var out = join( x, {
    'dims': [ 0 ]
});
// returns <ndarray>[ '1,3', '2,4' ]

out = join( x, {
    'dims': [ 1 ]
});
// returns <ndarray>[ '1,2', '3,4' ]

out = join( x, {
    'dims': [ 0, 1 ]
});
// returns <ndarray>[ '1,2,3,4' ]
```

By default, the function excludes reduced dimensions from the output [ndarray][@stdlib/ndarray/ctor]. To include the reduced dimensions as singleton dimensions, set the `keepdims` option to `true`.

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

var x = array( [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ] );

var opts = {
    'dims': [ 0 ],
    'keepdims': true
};

var out = join( x, opts );
// returns <ndarray>[ [ '1,3', '2,4' ] ]
```

#### join.assign( x, out\[, options] )

Joins elements of an input [ndarray][@stdlib/ndarray/ctor] using a separator along one or more [ndarray][@stdlib/ndarray/ctor] dimensions and assigns results to a provided output [ndarray][@stdlib/ndarray/ctor].

```javascript
var array = require( '@stdlib/ndarray/array' );
var scalar2ndarray = require( '@stdlib/ndarray/from-scalar' );

var x = array( [ 1.0, 2.0, 3.0, 4.0 ] );
var y = scalar2ndarray( '', {
    'dtype': 'generic'
});

var out = join.assign( x, y );
// returns <ndarray>[ '1,2,3,4' ]

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

The method has the following parameters:

-   **x**: input [ndarray][@stdlib/ndarray/ctor].
-   **out**: output [ndarray][@stdlib/ndarray/ctor].
-   **options**: function options (_optional_).

The method accepts the following options:

-   **sep**: separator. May be either a scalar value or an [ndarray][@stdlib/ndarray/ctor] having a "generic" [data type][@stdlib/ndarray/dtypes]. If provided an [ndarray][@stdlib/ndarray/ctor], the value must have a shape which is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with the complement of the shape defined by `options.dims`. For example, given the input shape `[2, 3, 4]` and `options.dims=[0]`, an [ndarray][@stdlib/ndarray/ctor] separator value must have a shape which is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with the shape `[3, 4]`. Similarly, when performing the operation over all elements in a provided input [ndarray][@stdlib/ndarray/ctor], an [ndarray][@stdlib/ndarray/ctor] separator value must be a zero-dimensional [ndarray][@stdlib/ndarray/ctor]. Default: `,`.
-   **dims**: list of dimensions over which to perform operation. If not provided, the function performs the operation over all elements in a provided input [ndarray][@stdlib/ndarray/ctor].

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   Setting the `keepdims` option to `true` can be useful when wanting to ensure that the output [ndarray][@stdlib/ndarray/ctor] is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with ndarrays having the same shape as the input [ndarray][@stdlib/ndarray/ctor].

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var ndarray = require( '@stdlib/ndarray/ctor' );
var join = require( '@stdlib/blas/ext/join' );

// Generate an array of random numbers:
var xbuf = discreteUniform( 10, 0, 20, {
    'dtype': 'float64'
});

// Wrap in an ndarray:
var x = new ndarray( 'float64', xbuf, [ 5, 2 ], [ 2, 1 ], 0, 'row-major' );
console.log( ndarray2array( x ) );

// Perform operation:
var out = join( x, {
    'dims': [ -1 ]
});

// Print the results:
console.log( ndarray2array( out ) );
```

</section>

<!-- /.examples -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="links">

[@stdlib/ndarray/ctor]: https://www.npmjs.com/package/@stdlib/ndarray-ctor

[@stdlib/ndarray/dtypes]: https://www.npmjs.com/package/@stdlib/ndarray-dtypes

[@stdlib/ndarray/base/broadcast-shapes]: https://www.npmjs.com/package/@stdlib/ndarray-base-broadcast-shapes

</section>

<!-- /.links -->
