# Help with Ruby code in Logstash
**URL:** https://discuss.elastic.co/t/help-with-ruby-code-in-logstash/142384
**Category:** Logstash
**Created:** [July 31, 2018, 2:21pm UTC](https://discuss.elastic.co/t/help-with-ruby-code-in-logstash/142384 "2018-07-31T14:21:32Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@espogian](https://discuss.elastic.co/u/espogian)
#### Post date: [July 31, 2018, 2:21pm UTC](https://discuss.elastic.co/t/help-with-ruby-code-in-logstash/142384/1 "2018-07-31T14:21:32Z")
Hi, I have to create a new field in a Logstash filter which should be the result of a math operation between two other fields.
Given that I have defined in input section:
```
convert => { "field1" => "integer" }
convert => { "field2" => "integer" }
```
I want to create `field3 = ( field1 - field2 ) / field1`
I tried with this Ruby code:
```
ruby { code => "field3= ( event.get['field1'] - event.get['field2'] ) \ event.get['field1'];
event.set['field3'] = field3" }
```
But this ends up in a error:
`[ERROR][org.logstash.Logstash] java.lang.IllegalStateException: Logstash stopped processing because of an error: (SyntaxError) (ruby filter code):2: syntax error, unexpected null`
What is going wrong?
---
### Author:  [@Badger](https://discuss.elastic.co/u/Badger)
#### Post date: [July 31, 2018, 2:41pm UTC](https://discuss.elastic.co/t/help-with-ruby-code-in-logstash/142384/2 "2018-07-31T14:41:47Z")
Try this
```
ruby {
code => "
field3 = ( event.get('field1').to_f - event.get('field2').to_f ) / event.get('field1').to_f;
event.set('field3', field3)
"
}
```
---
### Author:  [@espogian](https://discuss.elastic.co/u/espogian)
#### Post date: [July 31, 2018, 3:33pm UTC](https://discuss.elastic.co/t/help-with-ruby-code-in-logstash/142384/3 "2018-07-31T15:33:42Z")
@Badger thank you.
I would like to introduce a check in order to avoid the situation in which field1 is equal to zero.
Do you think this is the correct approach?
```
if [field1] > 0 {
ruby {
code => "
availability = ( event.get('field1').to_f - event.get('field2').to_f ) / event.get('field1').to_f;
event.set('field3', field3)
"
}
}
```
---
### Author:  [@Badger](https://discuss.elastic.co/u/Badger)
#### Post date: [July 31, 2018, 3:57pm UTC](https://discuss.elastic.co/t/help-with-ruby-code-in-logstash/142384/4 "2018-07-31T15:57:03Z")
That looks reasonable.
---
### Author:  [@espogian](https://discuss.elastic.co/u/espogian)
#### Post date: [August 7, 2018, 7:55am UTC](https://discuss.elastic.co/t/help-with-ruby-code-in-logstash/142384/5 "2018-08-07T07:55:31Z")
Hi @Badger, sorry for resuming this topic but I'm facing a little issue with the code:
```
if [field1] > 0
```
This produces this error:
```
"exception"=>"comparison of String with 0 failed"
```
The thing is strange because in the filter I have defined `field1` as integer:
```
convert => { "field1" => "integer" }
```
What am I missing?
---
### Author:  [@espogian](https://discuss.elastic.co/u/espogian)
#### Post date: [August 7, 2018, 8:18am UTC](https://discuss.elastic.co/t/help-with-ruby-code-in-logstash/142384/6 "2018-08-07T08:18:36Z")
I found the issue. This option here:
```
csv {
skip_header => "true"
```
Is not working. So Logstash is importing the header of the CSV and this makes some fields containing strings. Is this a known bug?
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [September 4, 2018, 8:18am UTC](https://discuss.elastic.co/t/help-with-ruby-code-in-logstash/142384/7 "2018-09-04T08:18:42Z")
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