How do I set relative bar width in altair?

user_5726347 0
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How do I use relative bar width with altair? According to vega-lite documentation. This code:

{
  "data": {"url": "data/seattle-weather.csv"},
  "mark": {"type": "bar", "width": {"band": 0.7}},
  "encoding": {
    "x": {
      "timeUnit": "month",
      "field": "date"
    },
    "y": {
      "aggregate": "mean",
      "field": "precipitation"
    }
  }
}

produces a bar that occupies 70% of each x band.

How do I set this in altair? If I use something like:

.mark_bar(width={'band':0.7})

I got an error about width not being a number.

How do I set relative bar widths in altair?

altair
2 Answers

You could also set the padding between the bars instead, using padding in the scale argument of the encoding field. For mark_bar, for example, setting it to 0.3, would set the bar width to 70% of the 'tick space'.

import altair as alt
from vega_datasets import data

source = data.seattle_weather()

alt.Chart(source).mark_bar().encode(
    x=alt.X('month(date):O', scale=alt.Scale(padding=0.3)),
    y='mean(precipitation):Q'    
)
user_136382190

On the current development version of Altair on GitHub, what you suggested should work. As per this post, you should also be able to do the following:

import altair as alt
from vega_datasets import data

source = data.seattle_weather()

alt.Chart(source).mark_bar(
    width=alt.RelativeBandSize(0.7)
).encode(
    x='month(date):O',
    y='mean(precipitation):Q'    
)
user_21668230
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