Usage

`javascript
var subBy = require( '@stdlib/math-strided-ops-sub-by' );
`

#### subBy( N, x, strideX, y, strideY, z, strideZ, clbk\[, thisArg] )

Performs element-wise [subtraction][@stdlib/number/float64/base/sub] of two strided arrays via a callback function and assigns each result to an element in an output strided array.

`javascript
function accessor( values ) {
return values;
}

var x = [ 11.0, 12.0, 13.0, 14.0, 15.0 ];
var y = [ 8.0, 7.0, 6.0, 5.0, 4.0 ];
var z = [ 0.0, 0.0, 0.0, 0.0, 0.0 ];

subBy( x.length, x, 1, y, 1, z, 1, accessor );
// z => [ 3.0, 5.0, 7.0, 9.0, 11.0 ]
`

The function accepts the following arguments:

- N: number of indexed elements.
- x: input [Array][mdn-array], [typed array][mdn-typed-array], or an array-like object (excluding strings and functions).
- strideX: index increment for x.
- y: input [Array][mdn-array], [typed array][mdn-typed-array], or an array-like object (excluding strings and functions).
- strideY: index increment for y.
- z: output [Array][mdn-array], [typed array][mdn-typed-array], or an array-like object (excluding strings and functions).
- strideZ: index increment for z.
- clbk: callback function.
- thisArg: execution context (_optional_).

The invoked callback function is provided four arguments:

- values: input array element values [vx, vy].
- idx: iteration index (zero-based).
- indices: input and output array strided indices [ix, iy, iz] (computed according to offset + idx*stride).
- arrays: input and output arrays/collections [x, y, z].

To set the callback execution context, provide a thisArg.

`javascript
function accessor( values ) {
this.count += 1;
return values;
}

var context = {
'count': 0
};

var x = [ 11.0, 12.0, 13.0, 14.0, 15.0 ];
var y = [ 8.0, 7.0, 6.0, 5.0, 4.0 ];
var z = [ 0.0, 0.0, 0.0, 0.0, 0.0 ];

subBy( x.length, x, 1, y, 1, z, 1, accessor, context );
// z => [ 3.0, 5.0, 7.0, 9.0, 11.0 ]

var cnt = context.count;
// returns 5
`

The N and stride parameters determine which elements in the strided arrays are accessed at runtime. For example, to index every other value in x and to index the first N elements of y in reverse order,

`javascript
function accessor( values ) {
return values;
}

var x = [ 11.0, 12.0, 13.0, 14.0, 15.0, 16.0 ];
var y = [ 8.0, 7.0, 6.0, 5.0, 4.0, 3.0 ];
var z = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

subBy( 3, x, 2, y, -1, z, 1, accessor );
// z => [ 5.0, 6.0, 7.0, 0.0, 0.0, 0.0 ]
`

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

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

function accessor( values ) {
return values;
}

// Initial arrays...
var x0 = new Float64Array( [ 11.0, 12.0, 13.0, 14.0, 15.0, 16.0 ] );
var y0 = new Float64Array( [ 8.0, 7.0, 6.0, 5.0, 4.0, 3.0 ] );
var z0 = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

// Create offset views...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element
var z1 = new Float64Array( z0.buffer, z0.BYTES_PER_ELEMENT*3 ); // start at 4th element

subBy( 3, x1, -2, y1, 1, z1, 1, accessor );
// z0 => [ 0.0, 0.0, 0.0, 11.0, 10.0, 9.0 ]
`

#### subBy.ndarray( N, x, strideX, offsetX, y, strideY, offsetY, z, strideZ, offsetZ, clbk\[, thisArg] )

Performs element-wise [subtraction][@stdlib/number/float64/base/sub] of two strided arrays via a callback function and assigns each result to an element in an output strided array using alternative indexing semantics.

`javascript
function accessor( values ) {
return values;
}

var x = [ 11.0, 12.0, 13.0, 14.0, 15.0 ];
var y = [ 8.0, 7.0, 6.0, 5.0, 4.0 ];
var z = [ 0.0, 0.0, 0.0, 0.0, 0.0 ];

subBy.ndarray( x.length, x, 1, 0, y, 1, 0, z, 1, 0, accessor );
// z => [ 3.0, 5.0, 7.0, 9.0, 11.0 ]
`

The function accepts the following additional arguments:

- offsetX: starting index for x.
- offsetY: starting index for y.
- offsetZ: starting index for z.

While [typed array][mdn-typed-array] views mandate a view offset based on the underlying buffer, the offset parameters support indexing semantics based on starting indices. For example, to index every other value in x starting from the second value and to index the last N elements in y,

`javascript
function accessor( values ) {
return values;
}

var x = [ 11.0, 12.0, 13.0, 14.0, 15.0, 16.0 ];
var y = [ 8.0, 7.0, 6.0, 5.0, 4.0, 3.0 ];
var z = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

subBy.ndarray( 3, x, 2, 1, y, -1, y.length-1, z, 1, 2, accessor );
// z => [ 0.0, 0.0, 0.0, 11.0, 10.0, 9.0 ]
`