# Canvas: filtering on mapped columns
**URL:** https://discuss.elastic.co/t/canvas-filtering-on-mapped-columns/169828
**Category:** Kibana
**Tags:** canvas
**Created:** [February 25, 2019, 12:29pm UTC](https://discuss.elastic.co/t/canvas-filtering-on-mapped-columns/169828 "2019-02-25T12:29:36Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@rozling](https://discuss.elastic.co/u/rozling)
#### Post date: [February 25, 2019, 12:29pm UTC](https://discuss.elastic.co/t/canvas-filtering-on-mapped-columns/169828/1 "2019-02-25T12:29:36Z")
I'm trying to use Canvas to map values so that different data sources can be filtered on a common, mapped column.
I would have expected that a DropDown Filter with a mapped column would filter the same values on the rest of my elements, but that doesn't seem to be working.
See the attached worksheet for an example of what I mean using the demo data; is it possible to filter on mapped columns like this, or am I expecting too much?
**Example**
A table using demo data:
```
filters
| demodata
| mapColumn "cool-project"
fn=${getCell "project" | switch
{case if={compare eq to="kibana"} then="KIB"}
{case if={compare eq to="logstash"} then="LOG"}
{case if={compare eq to="opbeat"} then="OPB"}
{case if={compare eq to="elasticsearch"} then="ELS"}
default="other"
}
| table
| render
```
A filter which I would expect to filter that table:
```
demodata
| mapColumn "cool-project"
fn=${getCell "project" | switch
{case if={compare eq to="kibana"} then="KIB"}
{case if={compare eq to="logstash"} then="LOG"}
{case if={compare eq to="opbeat"} then="OPB"}
{case if={compare eq to="elasticsearch"} then="ELS"}
default="other"
}
| dropdownControl valueColumn="cool-project" filterColumn="cool-project"
| render
```
**Full worksheet of example**
```
{
"name": "mapColumn Test",
"id": "workpad-6c44f576-2ce6-49ce-9c0d-59d12fc39b4f",
"width": 1080,
"height": 720,
"page": 0,
"pages": [
{
"id": "page-e45857cf-2426-4cef-b13e-4387a1728c8c",
"style": {
"background": "#fff"
},
"transition": {},
"elements": [
{
"id": "element-842b2f96-0aaa-4e51-a96f-6a7ff2394ac6",
"position": {
"left": 20,
"top": 20,
"width": 500,
"height": 50,
"angle": 0
},
"expression": "demodata\n| mapColumn \"cool-project\"\n fn=${getCell \"project\" | switch \n{case if={compare eq to=\"kibana\"} then=\"KIB\"}\n{case if={compare eq to=\"logstash\"} then=\"LOG\"}\n{case if={compare eq to=\"opbeat\"} then=\"OPB\"}\n{case if={compare eq to=\"elasticsearch\"} then=\"ELS\"}\n default=\"other\"\n }\n| dropdownControl valueColumn=\"cool-project\" filterColumn=\"cool-project\"\n| render",
"filter": ""
},
{
"id": "element-c7bba917-d8c1-40fe-8f10-37ce0a6608e3",
"position": {
"left": 63,
"top": 204,
"width": 971,
"height": 368,
"angle": 0
},
"expression": "filters\n| demodata\n| mapColumn \"cool-project\"\n fn=${getCell \"project\" | switch \n{case if={compare eq to=\"kibana\"} then=\"KIB\"}\n{case if={compare eq to=\"logstash\"} then=\"LOG\"}\n{case if={compare eq to=\"opbeat\"} then=\"OPB\"}\n{case if={compare eq to=\"elasticsearch\"} then=\"ELS\"}\n default=\"other\"\n }\n| table\n| render"
}
]
}
],
"colors": [
"#37988d",
"#c19628",
"#b83c6f",
"#3f9939",
"#1785b0",
"#ca5f35",
"#45bdb0",
"#f2bc33",
"#e74b8b",
"#4fbf48",
"#1ea6dc",
"#fd7643",
"#72cec3",
"#f5cc5d",
"#ec77a8",
"#7acf74",
"#4cbce4",
"#fd986f",
"#a1ded7",
"#f8dd91",
"#f2a4c5",
"#a6dfa2",
"#86d2ed",
"#fdba9f",
"#000000",
"#444444",
"#777777",
"#BBBBBB",
"#FFFFFF",
"rgba(255,255,255,0)"
],
"@timestamp": "2019-02-25T12:09:40.840Z",
"@created": "2019-02-25T12:05:16.417Z",
"assets": {}
}
```
---
### Author:  [@Joe\_Fleming](https://discuss.elastic.co/u/Joe_Fleming)
#### Post date: [March 1, 2019, 6:02pm UTC](https://discuss.elastic.co/t/canvas-filtering-on-mapped-columns/169828/2 "2019-03-01T18:02:50Z")
So conceptually, you're close, I think there's just a slight misunderstanding of how filters work here. Every function you use in the expression is "functional", meaning that if you provide it with the same input (context and arguments in Canvas terms), you will always get the same output. They also don't maintain any state, and no value is "global" in the expression.
The disconnect here is how `filters` works I think. That function produces a filters "context" that is passed into the next function, `demodata` in your case. For your dropdown filter, you've set `valueColumn="cool-project"` and `filterColumn="cool-project"`, meaning the dropdown will be populated with the values in the `cool-project` column. You also set `filterColumn="cool-project"`, so when the filter is applied, it will be "bound" to the `cool-project` column.
The reason this doesn't work is because `demodata` doesn't contain a `cool-project` column, so applying the filter will just remove all the rows, since none of them match. You need to somehow map that filter value back to the original data (ie. the contents of `demodata`).
The easiest option is to use the original values from demodata in the dropdown.
```auto
demodata
| dropdownControl valueColumn="project" filterColumn="project"
| render
```
That filter will work, you'll still see the `cool-project` values in the table, and you'll get the right results, but you won't see "KIB" and "LOG" in the dropdown, you'll see "kibana" and "logstash", which isn't really what you want.
You need a way to apply the filter value _after_ you use mapColumn, because `cool-project` doesn't exist until after that function. That's not something that exists today.
Alternatively, and I'm going to add this shortly now (thanks for the idea), we could enhance the dropdown filter with a new argument `displayValue`, so then you could have it show your mapped value but actually use the original source value behind the scenes, like this:
`| dropdownControl displayColumn=cool-project valueColumn=project filterColumn=project`
So you'll see your `cool-project` value, but when you pick something, it'll _actually_ apply the `project` value and do what you expect. I created this issue to track the enhancement, and I may have explained it better there: [https://github.com/elastic/kibana/issues/32331](https://github.com/elastic/kibana/issues/32331)
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [March 29, 2019, 6:02pm UTC](https://discuss.elastic.co/t/canvas-filtering-on-mapped-columns/169828/3 "2019-03-29T18:02:51Z")
This topic was automatically closed 28 days after the last reply. New replies are no longer allowed.