# Document Index

Use the `documentIndex` operator (or the `di` shorthand) to select nodes of a particular document.

## Retrieve a document index

Given a sample.yml file of:

```yaml
a: cat
---
a: frog
```

then

```bash
yq '.a | document_index' sample.yml
```

will output

```yaml
0
---
1
```

## Retrieve a document index, shorthand

Given a sample.yml file of:

```yaml
a: cat
---
a: frog
```

then

```bash
yq '.a | di' sample.yml
```

will output

```yaml
0
---
1
```

## Filter by document index

Given a sample.yml file of:

```yaml
a: cat
---
a: frog
```

then

```bash
yq 'select(document_index == 1)' sample.yml
```

will output

```yaml
a: frog
```

## Filter by document index shorthand

Given a sample.yml file of:

```yaml
a: cat
---
a: frog
```

then

```bash
yq 'select(di == 1)' sample.yml
```

will output

```yaml
a: frog
```

## Print Document Index with matches

Given a sample.yml file of:

```yaml
a: cat
---
a: frog
```

then

```bash
yq '.a | ({"match": ., "doc": document_index})' sample.yml
```

will output

```yaml
match: cat
doc: 0
---
match: frog
doc: 1
```