# Subtract

You can use subtract to subtract numbers as well as remove elements from an array.

## Array subtraction

Running

```bash
yq --null-input '[1,2] - [2,3]'
```

will output

```yaml
- 1
```

## Array subtraction with nested array

Running

```bash
yq --null-input '[[1], 1, 2] - [[1], 3]'
```

will output

```yaml
- 1
- 2
```

## Array subtraction with nested object

Note that order of the keys does not matter

Given a sample.yml file of:

```yaml
- a: b
  c: d
- a: b
```

then

```bash
yq '. - [{"c": "d", "a": "b"}]' sample.yml
```

will output

```yaml
- a: b
```

## Number subtraction - float

If the lhs or rhs are floats then the expression will be calculated with floats.

Given a sample.yml file of:

```yaml
a: 3
b: 4.5
```

then

```bash
yq '.a = .a - .b' sample.yml
```

will output

```yaml
a: -1.5
b: 4.5
```

## Number subtraction - int

If both the lhs and rhs are ints then the expression will be calculated with ints.

Given a sample.yml file of:

```yaml
a: 3
b: 4
```

then

```bash
yq '.a = .a - .b' sample.yml
```

will output

```yaml
a: -1
b: 4
```

## Decrement numbers

Given a sample.yml file of:

```yaml
a: 3
b: 5
```

then

```bash
yq '.[] -= 1' sample.yml
```

will output

```yaml
a: 2
b: 4
```

## Date subtraction

You can subtract durations from dates. Assumes RFC3339 date time format, see [date-time operators](https://mikefarah.gitbook.io/yq/operators/date-time-operators) for more information.

Given a sample.yml file of:

```yaml
a: 2021-01-01T03:10:00Z
```

then

```bash
yq '.a -= "3h10m"' sample.yml
```

will output

```yaml
a: 2021-01-01T00:00:00Z
```

## Date subtraction - custom format

Use with\_dtf to specify your datetime format. See [date-time operators](https://mikefarah.gitbook.io/yq/operators/date-time-operators) for more information.

Given a sample.yml file of:

```yaml
a: Saturday, 15-Dec-01 at 6:00AM GMT
```

then

```bash
yq 'with_dtf("Monday, 02-Jan-06 at 3:04PM MST", .a -= "3h1m")' sample.yml
```

will output

```yaml
a: Saturday, 15-Dec-01 at 2:59AM GMT
```

## Custom types: that are really numbers

When custom tags are encountered, yq will try to decode the underlying type.

Given a sample.yml file of:

```yaml
a: !horse 2
b: !goat 1
```

then

```bash
yq '.a -= .b' sample.yml
```

will output

```yaml
a: !horse 1
b: !goat 1
```


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