Forum Discussion
Vega Lite - scatter plot
Hi Everyone.
Simple question 😉
How in Vega Lite draw line/rule (x=y) on scatterplot chart (basically line in 45 degrees)
8 Replies
Find the max x and y values in your data, take the largest, and then add a layer that draws from 0 to that point.
Here is a simplified version:
{ "layer": [ { "data": {"name": "dataset"}, "mark": "point", "encoding": { "y": { "field": "y", "type": "quantitative" }, "x": { "field": "x", "type": "quantitative" } } }, { "data": { "values": [ {"x": 0, "y": 0}, {"x": 4, "y": 4} ] }, "mark": { "type": "line", "from": {"data": "data2"} }, "encoding": { "y": { "field": "y", "type": "quantitative" }, "x": { "field": "x", "type": "quantitative" } } } ] }You can do that in DAX, and add it as a column in the Deneb visual.
I can but I have like 150k points on the chart. Any additional data will have a huge impact on the performance
Hi AdamMG,
If you just want to draw a line across the width/height of the visible view, you can do something like this, where you create a layer with a simple, empty dataset (like the fixed line example) :{ "$schema": "https://vega.github.io/schema/vega-lite/v5.json", "data": {"url": "data/cars.json"}, "layer": [ { "data": {"values": [{}]}, "mark": "rule", "encoding": { "x": {"value": 0}, "x2": {"value": "width"}, "y": {"value": "height"}, "y2": {"value": 0} } }, { "mark": "point", "encoding": { "x": {"field": "Horsepower"}, "y": {"field": "Miles_per_Gallon"} } } ], "encoding": {"x": {"type": "quantitative"}, "y": {"type": "quantitative"}} }You could also use the expression language to interrogate the assigned scale domains, e.g.:
{ "$schema": "https://vega.github.io/schema/vega-lite/v5.json", "data": {"url": "data/cars.json"}, "layer": [ { "data": {"values": [{}]}, "mark": "rule", "encoding": { "x": {"datum": {"expr": "domain('x')[0]"}}, "x2": {"datum": {"expr": "domain('x')[1]"}}, "y": {"datum": {"expr": "domain('y')[0]"}}, "y2": {"datum": {"expr": "domain('y')[1]"}} } }, { "mark": "point", "encoding": { "x": {"field": "Horsepower"}, "y": {"field": "Miles_per_Gallon"} } } ], "encoding": {"x": {"type": "quantitative"}, "y": {"type": "quantitative"}} }
If you want to do something fancier with the range of data for each encoding channel, this may be possible but would require a sample of your dataset to ensure that I could come up with an optimal approach. If you're not able to share, you might be able to consider an aggregate transform, to find the min/max of each series and plot based on those, or possibly a regression transform may be an option.Hopefully, some of this may help you come up with more ideas. And thanks very much for trying Deneb!
Regards,
Daniel
