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<h1 id="function-subset">Function subset <a href="#function-subset" title="Permalink">#</a></h1>

Get or set a subset of a matrix or string.


<h2 id="syntax">Syntax <a href="#syntax" title="Permalink">#</a></h2>

```js
math.subset(value, index)                                // retrieve a subset
math.subset(value, index, replacement [, defaultValue])  // replace a subset
```

<h3 id="parameters">Parameters <a href="#parameters" title="Permalink">#</a></h3>

Parameter | Type | Description
--------- | ---- | -----------
`matrix` | Array &#124; Matrix &#124; string | An array, matrix, or string
`index` | Index |  For each dimension of the target, specifies an index or a list of indices to fetch or set. `subset` uses the cartesian product of the indices specified in each dimension.
`replacement` | * | An array, matrix, or scalar. If provided, the subset is replaced with replacement. If not provided, the subset is returned
`defaultValue` | * | Default value, filled in on new entries when the matrix is resized. If not provided, math.matrix elements will be left undefined. Default value: undefined.

<h3 id="returns">Returns <a href="#returns" title="Permalink">#</a></h3>

Type | Description
---- | -----------
Array &#124; Matrix &#124; string | Either the retrieved subset or the updated matrix.


<h3 id="throws">Throws <a href="#throws" title="Permalink">#</a></h3>

Type | Description
---- | -----------


<h2 id="examples">Examples <a href="#examples" title="Permalink">#</a></h2>

```js
// get a subset
const d = [[1, 2], [3, 4]]
math.subset(d, math.index(1, 0))             // returns 3
math.subset(d, math.index([0, 1], 1))        // returns [[2], [4]]
math.subset(d, math.index([false, true], 0)) // returns [[3]]

// replace a subset
const e = []
const f = math.subset(e, math.index(0, [0, 2]), [5, 6])  // f = [[5, 0, 6]]
const g = math.subset(f, math.index(1, 1), 7, 0)         // g = [[5, 0, 6], [0, 7, 0]]
math.subset(g, math.index([false, true], 1), 8)          // returns [[5, 0, 6], [0, 8, 0]]

// get submatrix using ranges
const M = [
  [1,2,3],
  [4,5,6],
  [7,8,9]
]
math.subset(M, math.index(math.range(0,2), math.range(0,3))) // [[1, 2, 3], [4, 5, 6]]
```


<h2 id="see-also">See also <a href="#see-also" title="Permalink">#</a></h2>

[size](size.html),
[resize](resize.html),
[squeeze](squeeze.html),
[index](index.html)