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# gindexOfColumn

> Return the index of the first column in an input matrix which has the same elements as a provided search vector.

<section class="usage">

## Usage

```javascript
var gindexOfColumn = require( '@stdlib/blas/ext/base/gindex-of-column' );
```

#### gindexOfColumn( order, M, N, A, LDA, x, strideX )

Returns the index of the first column in an input matrix which has the same elements as a provided search vector.

```javascript
/*
    A = [
        [ 1.0, 2.0 ],
        [ 3.0, 4.0 ],
        [ 0.0, 0.0 ]
    ]
*/
var A = [ 1.0, 2.0, 3.0, 4.0, 0.0, 0.0 ];

var x = [ 2.0, 4.0, 0.0 ];
var out = gindexOfColumn( 'row-major', 3, 2, A, 2, x, 1 );
// returns 1
```

The function has the following parameters:

-   **order**: storage layout.
-   **M**: number of rows in `A`.
-   **N**: number of columns in `A`.
-   **A**: input matrix as a linear array.
-   **LDA**: stride of the first dimension of `A` (a.k.a., leading dimension of the matrix `A`).
-   **x**: search vector.
-   **strideX**: stride length of `x`.

If the function is unable to find a matching column, the function returns `-1`.

```javascript
var A = [ 1.0, 2.0, 3.0, 4.0, 0.0, 0.0 ];

var x = [ -2.0, -4.0, 0.0 ];
var out = gindexOfColumn( 'row-major', 3, 2, A, 2, x, 1 );
// returns -1
```

Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.

<!-- eslint-disable stdlib/capitalized-comments -->

```javascript
var Float64Array = require( '@stdlib/array/float64' );

// Initial arrays:
var A0 = new Float64Array( [ 9999.0, 1.0, 2.0, 3.0, 4.0, 0.0, 0.0 ] );
var x0 = new Float64Array( [ 9999.0, 2.0, 4.0, 0.0 ] );

// Create offset views:
var A1 = new Float64Array( A0.buffer, A0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

var out = gindexOfColumn( 'row-major', 3, 2, A1, 2, x1, 1 );
// returns 1
```

<!-- lint disable maximum-heading-length -->

#### gindexOfColumn.ndarray( M, N, A, strideA1, strideA2, offsetA, x, strideX, offsetX )

<!-- lint enable maximum-heading-length -->

Returns the index of the first column in an input matrix which has the same elements as a provided search vector using alternative indexing semantics.

```javascript
/*
    A = [
        [ 1.0, 2.0 ],
        [ 3.0, 4.0 ],
        [ 0.0, 0.0 ]
    ]
*/
var A = [ 1.0, 2.0, 3.0, 4.0, 0.0, 0.0 ];

var x = [ 2.0, 4.0, 0.0 ];
var out = gindexOfColumn.ndarray( 3, 2, A, 2, 1, 0, x, 1, 0 );
// returns 1
```

The function has the following parameters:

-   **M**: number of rows in `A`.
-   **N**: number of columns in `A`.
-   **A**: input matrix as a linear array.
-   **strideA1**: stride of the first dimension of `A`.
-   **strideA2**: stride of the second dimension of `A`.
-   **offsetA**: starting index for `A`.
-   **x**: search vector.
-   **strideX**: stride length of `x`.
-   **offsetX**: starting index for `x`.

While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying buffer, offset parameters support indexing semantics based on starting indices. For example,

```javascript
/*
    A = [
        [ 1.0, 2.0 ],
        [ 3.0, 4.0 ],
        [ 0.0, 0.0 ]
    ]
*/
var A = [ 9999.0, 1.0, 2.0, 3.0, 4.0, 0.0, 0.0 ];

var x = [ 9999.0, 2.0, 4.0, 0.0 ];
var out = gindexOfColumn.ndarray( 3, 2, A, 2, 1, 1, x, 1, 1 );
// returns 1
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   When searching for a matching column, the function checks for equality using the strict equality operator `===`. As a consequence, `NaN` values are considered distinct, and `-0` and `+0` are considered the same.
-   Both functions support array-like objects having getter and setter accessors for array element access (e.g., [`@stdlib/array/base/accessor`][@stdlib/array/base/accessor]).

</section>

<!-- /.notes -->

<section class="examples">

## Examples

<!-- eslint-disable max-len -->

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

```javascript
var ndarray2array = require( '@stdlib/ndarray/base/to-array' );
var shape2strides = require( '@stdlib/ndarray/base/shape2strides' );
var gindexOfColumn = require( '@stdlib/blas/ext/base/gindex-of-column' );

var shape = [ 3, 3 ];
var order = 'row-major';
var strides = shape2strides( shape, order );

var A = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0 ];
console.log( ndarray2array( A, shape, strides, 0, order ) );

var x = [ 2.0, 5.0, 8.0 ];
console.log( x );

var out = gindexOfColumn( order, shape[ 0 ], shape[ 1 ], A, strides[ 0 ], x, 1, 0 );
console.log( 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">

[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray

[@stdlib/array/base/accessor]: https://www.npmjs.com/package/@stdlib/array-base-accessor

</section>

<!-- /.links -->
