# My own logstash filter doesn't extract the input field value correctly
**URL:** https://discuss.elastic.co/t/my-own-logstash-filter-doesnt-extract-the-input-field-value-correctly/59803
**Category:** Logstash
**Created:** [September 5, 2016, 11:17am UTC](https://discuss.elastic.co/t/my-own-logstash-filter-doesnt-extract-the-input-field-value-correctly/59803 "2016-09-05T11:17:25Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@sen](https://discuss.elastic.co/u/sen)
#### Post date: [September 5, 2016, 11:17am UTC](https://discuss.elastic.co/t/my-own-logstash-filter-doesnt-extract-the-input-field-value-correctly/59803/1 "2016-09-05T11:17:25Z")
Hello folks,
I have built my own plugin filter for logstash. The principle of this
filter is to get some coordinates (x,y) formated in a coordinates
system called "lambertII" and to convert them in gps system (latitude,
longitude). Here is an example:
```
lambert {
convert => ["lambertII", x, y]
latitude => ["lat"] #return as output latitude
longitude => ["long"] #return as output longitude
}
```
It works well when I write for instance:
```
convert => ["LambertII", 2478517.33, 547536.68]
```
However, when I extract data from a json file as shown below
```
{"x":2478517.33, "y":547536.68}
{"x":2699120.65, "y":544959.56}
```
but it does not work, when I write:
```
convert => ["LambertII", "%{[x]}", "%{[y]}"]
```
or
```
convert => ["LambertII", "%{x}", "%{y}"]
```
Indeed, my ruby code does not extract the float value from the
expressions "%{[..]}" or "%{..}" but it interprets them like string
expressions.
I have already seen this following link but it didn't solve my problem: [https://www.elastic.co/guide/en/logstash/current/event-dependent-configuration.html#event-dependent-configuration](https://www.elastic.co/guide/en/logstash/current/event-dependent-configuration.html#event-dependent-configuration)
I didn't find out how to solve this problem. I would be very thankful for any help.
Thank you for your attention and your help !
PS: I can provide my ruby code lambert.rb if it is usefull
---
### Author:  [@magnusbaeck](https://discuss.elastic.co/u/magnusbaeck)
#### Post date: [September 5, 2016, 11:40am UTC](https://discuss.elastic.co/t/my-own-logstash-filter-doesnt-extract-the-input-field-value-correctly/59803/2 "2016-09-05T11:40:44Z")
It seems you're not calling event.sprintf() on the field values.
---
### Author:  [@sen](https://discuss.elastic.co/u/sen)
#### Post date: [September 5, 2016, 11:57am UTC](https://discuss.elastic.co/t/my-own-logstash-filter-doesnt-extract-the-input-field-value-correctly/59803/3 "2016-09-05T11:57:41Z")
thank you very much Magnus, I was so stuck 😃 !
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [July 6, 2017, 4:39am UTC](https://discuss.elastic.co/t/my-own-logstash-filter-doesnt-extract-the-input-field-value-correctly/59803/4 "2017-07-06T04:39:54Z")