yq/pkg/yqlib/doc/operators/unique.md

# Unique

This is used to filter out duplicated items in an array. Note that the original order of the array is maintained.


## Unique array of scalars (string/numbers)
Note that unique maintains the original order of the array.

Given a sample.yml file of:
```yaml
[2, 1, 3, 2]
```
then
```bash
yq 'unique' sample.yml
```
will output
```yaml
[2, 1, 3]
```

## Unique nulls
Unique works on the node value, so it considers different representations of nulls to be different

Given a sample.yml file of:
```yaml
[~, null, ~, null]
```
then
```bash
yq 'unique' sample.yml
```
will output
```yaml
[~, null]
```

## Unique all nulls
Run against the node tag to unique all the nulls

Given a sample.yml file of:
```yaml
[~, null, ~, null]
```
then
```bash
yq 'unique_by(tag)' sample.yml
```
will output
```yaml
[~]
```

## Unique array object fields
Given a sample.yml file of:
```yaml
[{name: harry, pet: cat}, {name: billy, pet: dog}, {name: harry, pet: dog}]
```
then
```bash
yq 'unique_by(.name)' sample.yml
```
will output
```yaml
[{name: harry, pet: cat}, {name: billy, pet: dog}]
```