mathjs/docs/reference/functions/filter.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 filter

Filter the items in an array or one dimensional matrix.


## Syntax

```js
math.filter(x, test)
```

### Parameters

Parameter | Type | Description
--------- | ---- | -----------
`x` | Matrix &#124; Array | A one dimensional matrix or array to filter
`test` | Function &#124; RegExp |  A function or regular expression to test items. All entries for which `test` returns true are returned. When `test` is a function, it is invoked with three parameters: the value of the element, the index of the element, and the matrix/array being traversed. The function must return a boolean.

### Returns

Type | Description
---- | -----------
Matrix &#124; Array | Returns the filtered matrix.


## Examples

```js
function isPositive (x) {
  return x > 0
}
math.filter([6, -2, -1, 4, 3], isPositive) // returns [6, 4, 3]

math.filter(["23", "foo", "100", "55", "bar"], /[0-9]+/) // returns ["23", "100", "55"]
```


## See also

[forEach](forEach.md),
[map](map.md),
[sort](sort.md)