How to put errorbars on only one group in plotnine?

Question

How do I put error bars on only one group in plotnine?

For example, say I have a dataframe:

dat = pd.DataFrame(data={"Type":["A","A","B","B"],"x":[1,2,1,2],"y":[1,2,2,4]}) 

Type  x  y
0    A  1  1
1    A  2  2
2    B  1  2
3    B  2  4

I can then plot two lines:

ggplot(dat,aes(x="x",y="y",linetype="Type")) + geom_line()

How woudld I then only add errorbars to A? Or more generally, how do I specify a subset of data in plotnine in subsequent additions to the plot?

Answer 1

Each geom layer has a data= argument which allows to specify the data to be used for this layer, whether from a second dataset or a subset of the global data, i.e. if you want to use only a subset of our data pass a filtered dataset to the data= argument.

import pandas as pd
from plotnine import *

dat = pd.DataFrame(data={"Type":["A","A","B","B"],"x":[1,2,1,2],"y":[1,2,2,4]})

ggplot(dat,aes(x="x",y="y",linetype="Type")) + \
    geom_line() + \
    geom_errorbar(
        aes(ymin="y-.5", ymax="y+.5"), 
        data = dat[dat["Type"] == "A"], 
        width = .1)