mathjs/docs/reference/functions/partitionSelect.md

Math.js is an extensive math library for JavaScript and Node.js. It features a flexible expression parser with support for symbolic computation, comes with a large set of built-in functions and constants, and offers an integrated solution to work with dif

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# Function partitionSelect

Partition-based selection of an array or 1D matrix.
Will find the kth smallest value, and mutates the input array.
Uses Quickselect.


## Syntax

```js
math.partitionSelect(x, k)
math.partitionSelect(x, k, compare)
```

### Parameters

Parameter | Type | Description
--------- | ---- | -----------
`x` | Matrix &#124; Array | A one dimensional matrix or array to sort
`k` | Number | The kth smallest value to be retrieved zero-based index
`compare` | Function &#124; 'asc' &#124; 'desc' |  An optional comparator function. The function is called as `compare(a, b)`, and must return 1 when a > b, -1 when a < b, and 0 when a == b. Default value: 'asc'.

### Returns

Type | Description
---- | -----------
* | Returns the kth lowest value.


## Examples

```js
math.partitionSelect([5, 10, 1], 2)           // returns 10
math.partitionSelect(['C', 'B', 'A', 'D'], 1) // returns 'B'

function sortByLength (a, b) {
  return a.length - b.length
}
math.partitionSelect(['Langdon', 'Tom', 'Sara'], 2, sortByLength) // returns 'Langdon'
```


## See also

[sort](sort.md)