Matt Matt - 3 years ago 239
Python Question

Adding error bars on top of bar charts in Bokeh

I am trying to create bar chart with error bars on top. I looked at the following answer to generate such view. My code works until I do

p.line(y_err_x, y_err_y, color="black" )
presumably due to
x
axis indexing as I get the following error:
Unable to get property 'A' of undefined or null reference


What is the appropriate use? Thanks in advance!

from bokeh.io import show, output_notebook
from bokeh.models import ColumnDataSource
from bokeh.plotting import figure
from bokeh.transform import factor_cmap

output_notebook()
groups= ['A', 'B', 'C', 'D']
counts = [5, 3, 4, 2]
yerr = [1,2,3,4]

source = ColumnDataSource(data=dict(groups=groups, counts=counts))

p = figure(x_range=groups, plot_height=350, toolbar_location=None, title="Values")
p.vbar(x='groups', top='counts', width=0.9, source=source, legend="groups",
line_color='white', fill_color=factor_cmap('groups', palette=["#962980","#295f96","#29966c","#968529"],
factors=groups))

y_err_x = []
y_err_y = []
for px, py, err in zip(groups, counts, yerr):
y_err_x.append((px, px))
y_err_y.append((py - err, py + err))

p.line(y_err_x, y_err_y, color="black" )

p.xgrid.grid_line_color = None
p.legend.orientation = "horizontal"
p.legend.location = "top_center"

show(p)

Answer Source

The technique of that answer is no longer necessary. Error annotations are now built into Bokeh, see the documentation:

https://bokeh.pydata.org/en/latest/docs/user_guide/annotations.html#whiskers

and

https://bokeh.pydata.org/en/latest/docs/user_guide/annotations.html#bands

Here is a complete example:

from bokeh.io import show, output_file
from bokeh.models import ColumnDataSource, Whisker
from bokeh.plotting import figure
from bokeh.transform import factor_cmap

output_file("error.html")

groups= ['A', 'B', 'C', 'D']
counts = [5, 3, 4, 2]
error = [0.8, 0.4, 0.4, 0.3]
upper = [x+e for x,e in zip(counts, error) ]
lower = [x-e for x,e in zip(counts, error) ]

source = ColumnDataSource(data=dict(groups=groups, counts=counts, upper=upper, lower=lower))

p = figure(x_range=groups, plot_height=350, toolbar_location=None, title="Values", y_range=(0,7))
p.vbar(x='groups', top='counts', width=0.9, source=source, legend="groups",
       line_color='white', fill_color=factor_cmap('groups', palette=["#962980","#295f96","#29966c","#968529"],
                                                  factors=groups))

p.add_layout(
    Whisker(source=source, base="groups", upper="upper", lower="lower", level="overlay")
)

p.xgrid.grid_line_color = None
p.legend.orientation = "horizontal"
p.legend.location = "top_center"

show(p)

enter image description here

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