# Replacing empty string with dynamic value from the same field

**URL:** <https://discuss.elastic.co/t/replacing-empty-string-with-dynamic-value-from-the-same-field/236686>\
**Category:** Logstash\
**Created:** [June 11, 2020, 11:04am UTC](https://discuss.elastic.co/t/replacing-empty-string-with-dynamic-value-from-the-same-field/236686 "2020-06-11T11:04:43Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![guas5](https://avatars.discourse-cdn.com/v4/letter/g/977dab/32.png) [@guas5](https://discuss.elastic.co/u/guas5)\
**Post date:** [June 11, 2020, 11:04am UTC](https://discuss.elastic.co/t/replacing-empty-string-with-dynamic-value-from-the-same-field/236686/1 "2020-06-11T11:04:44Z")

</div>

Hi everyone,

I would be grateful for your help regarding how to replace an empty string in a field witha dynamic value. I've already tried different filters such as replace, copy, etc. but it doesn't work as needed. Here is a log example:

2020-07-05 16:43:30.945 [INFO] Product Name: Table  
2020-07-05 16:43:30.947 [INFO] Product Material: Wood  
2020-07-05 16:43:30.948 [ERROR] Product Color: White

After using GROK filter, I have the following output:  
Timestamp logLevel ProductType  
2020-07-05 16:43:30.945 [INFO] Table  
2020-07-05 16:43:30.947 [INFO] -  
2020-07-05 16:43:30.948 [ERROR] -

I'm trying to replace empty string with the productType in order to be able to filter out all relevant information for a particular product based on its type. productType itself appears only ones in the whole log. Currently it doesn't work possibly because of timestamp and since productType is a dynamic field and might be different each time, so I can't assign a static value.  
I would be grateful for any ideas on how to do it maybe using lookup or ruby codec.

Desired output would be:

Timestamp logLevel ProductType  
2020-07-05 16:43:30.945 [INFO] Table  
2020-07-05 16:43:30.947 [INFO] Table  
2020-07-05 16:43:30.948 [ERROR] Table

Then comes the nex log and it works similarly but for another ProductType  
2020-07-05 17:31:30.945 [INFO] Chair  
2020-07-05 17:31:30.947 [INFO] Chair  
2020-07-05 17:32:30.948 [ERROR] Chair

Thank you!

---

<div class="post-metadata">

**Author:** ![Jenni](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/jenni/32/29684_2.png) [@Jenni](https://discuss.elastic.co/u/Jenni)\
**Post date:** [June 11, 2020, 12:00pm UTC](https://discuss.elastic.co/t/replacing-empty-string-with-dynamic-value-from-the-same-field/236686/2 "2020-06-11T12:00:31Z")

</div>

If I've got that right, you want to fill an empty field in the following events with the existing value from a previous event. Then your best bet would probably be to use only one worker thread and an [aggregate filter](https://www.elastic.co/guide/en/logstash/current/plugins-filters-aggregate.html).

When the value exists, you save it in the map. When it doesn't, you take it from the map.

---

<div class="post-metadata">

**Author:** ![guas5](https://avatars.discourse-cdn.com/v4/letter/g/977dab/32.png) [@guas5](https://discuss.elastic.co/u/guas5)\
**Post date:** [June 11, 2020, 12:39pm UTC](https://discuss.elastic.co/t/replacing-empty-string-with-dynamic-value-from-the-same-field/236686/3 "2020-06-11T12:39:07Z")

</div>

Hi Jenni,

Thanks for your idea and help. Yes, you got it right, I need to use the value from the previous event. Regarding the aggregate option I was hesitating since in each log will be a different value and logs will be ingested continiously. And on the web site there is a comment that "events might be processed out of sequence".  
If I understand you correctly, it should look like this:  
filter {  
if "ProductType" in [message] {  
grok { match =\> { [message] =\> "%{TIMESTAMP\_ISO8601:timestamp} ... %{WORD:productType}"}  
}  
if [productType] != "" {  
aggregate {  
productTypeFinal =\> "%{productType}"  
code =\> "map['productTypeFinal']=0"  
map\_action =\> "create"  
}  
....  
map\_action =\>"update"  
}  
}

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [July 9, 2020, 12:51pm UTC](https://discuss.elastic.co/t/replacing-empty-string-with-dynamic-value-from-the-same-field/236686/4 "2020-07-09T12:51:15Z")

</div>

This topic was automatically closed 28 days after the last reply. New replies are no longer allowed.