# `setIntersection`

## Description

Returns the intersection of two arrays, producing a new array with elements common to both.

- Both arrays are treated as sets:
- Duplicates are removed from both arrays
- Order is not preserved in the result
- `null` is treated as an empty set
- Supported element types include `string`, `bool`, `number`, `interval`, `timestamp`, `regexp`, and `enum`.

## Syntax

Like many functions in DataPrime, `setIntersection` supports [two notations](https://coralogix.com/docs/dataprime/language-reference/functions-reference/index.md), **function** and **method** notation. These interchangeable forms allow flexibility in how you structure expressions.

```dataprime
setIntersection(array1: array<T>, array2: array<T>): array<T>
```

```dataprime
(array1: array<T>).setIntersection(array2: array<T>): array<T>
```

## Arguments

| Name   | Type  | Required | Description                 |
| ------ | ----- | -------- | --------------------------- |
| array1 | array | **true** | The first array to compare  |
| array2 | array | **true** | The second array to compare |

## Example

**Use case: Compare observed IPs against a block list**

Suppose you collect IP addresses accessing different paths. Consider the following input:

```json
{
    "path": "/home",
    "ip_addresses": ["156.76.87.4", "156.76.12.4", "156.74.1.4"]
},
{
    "path": "/checkout",
    "ip_addresses": ["156.76.87.4"]
}
```

By applying `setIntersection`, you can identify which observed IP addresses also appear in a known block list.

### Example query

```dataprime
create unauthorized_ip_addresses from setIntersection(ip_addresses, ["156.76.12.4", "156.76.87.4"])
```

```dataprime
create unauthorized_ip_addresses from ip_addresses.setIntersection(["156.76.12.4", "156.76.87.4"])
```

### Example output

The result will include a new field `unauthorized_ip_addresses` showing IPs found in both arrays:

```json
{
    "path": "/home",
    "ip_addresses": ["156.76.87.4", "156.76.12.4", "156.74.1.4"],
    "unauthorized_ip_addresses": ["156.76.87.4", "156.76.12.4"]
},
{
    "path": "/checkout",
    "ip_addresses": ["156.76.87.4"],
    "unauthorized_ip_addresses": []
}
```