# Change value of a datum field using signal
**URL:** https://discuss.elastic.co/t/change-value-of-a-datum-field-using-signal/273158
**Category:** Kibana
**Tags:** vega
**Created:** [May 17, 2021, 10:15am UTC](https://discuss.elastic.co/t/change-value-of-a-datum-field-using-signal/273158 "2021-05-17T10:15:23Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Dzious](https://discuss.elastic.co/u/Dzious)
#### Post date: [May 17, 2021, 10:15am UTC](https://discuss.elastic.co/t/change-value-of-a-datum-field-using-signal/273158/1 "2021-05-17T10:15:24Z")
Hi,
I'm trying to have data that are relative to each one of my data. I've tried to use signal's data but i didn't managed to make them relative to one and only one value of my data.
i decided to add a field in my data values. now i'm trying to change the value of this field but i can't find a way to do so.
I've tried :
```auto
"signals": [
{
"name": "color_changer",
"value": "",
"on": [
{
"events": "rect:click",
"update": "datum.color === 'red' ? datum.color ='white' : datum.color ='red'"
}
]
}
],
```
But this does not work and result in a parsing error.
if anyone has an idea, some help would be appreciate. Thanks by advance.
---
### Author:  [@cheiligers](https://discuss.elastic.co/u/cheiligers)
#### Post date: [May 25, 2021, 8:00pm UTC](https://discuss.elastic.co/t/change-value-of-a-datum-field-using-signal/273158/2 "2021-05-25T20:00:13Z")
@Dzious Thanks for the question!
I'm not familiar with Vega but I think going through the Vega docs for [`signals`](https://vega.github.io/vega/docs/signals/) and [`expressions`](https://vega.github.io/vega/docs/expressions/) might help you out here.
I've used the examples from those docs in the past and they work great!
---
### Author:  [@Dzious](https://discuss.elastic.co/u/Dzious)
#### Post date: [May 26, 2021, 6:03am UTC](https://discuss.elastic.co/t/change-value-of-a-datum-field-using-signal/273158/3 "2021-05-26T06:03:51Z")
Hi @cheiligers,
Thanks for your help.
Unfortunately, due to technical limitations i've had to gave up the visualisation i was trying to build.
Since this vega was designed for a real time data visualisation, this means it would be needed to refresh it every X seconds making it impossible to save the state of each component between two refreshes
Still that's good to know and i'll have a look at it later on
Once again thanks and have a great day
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [June 23, 2021, 6:04am UTC](https://discuss.elastic.co/t/change-value-of-a-datum-field-using-signal/273158/4 "2021-06-23T06:04:10Z")
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