Bar graph with additional lines

Dash Python
1

Hi there,

I’m wondering if it’s possible to add horizontal lines for specific bars in a bar chart. I’ve attached a random bar plot with added red lines here. Essentially I would like to add a dotted line that shows a specific value for each bar. Any ideas? Thanks in advance!

ex
ex721×447 103 KB

2

Hello,

Are you looking for arbitrary lines or do they actually mean something in your data.

You could just utilize the stacked/grouped bar graph in both plotly.express or plotly.graph_objects if the lines mean something in your data.

If you’re just trying to to make some arbitrary lines you could do the following:

import plotly.graph_objects as go

animals=['giraffes', 'orangutans', 'monkeys']

fig = go.Figure(
            data=[
                go.Bar(x=animals, y=[12, 14, 21],showlegend=False), #This would be the "lines" . Set showlegend=False so this trace won't show in legend
                go.Bar(name='SF Zoo', x=animals, y=[25, 18, 33]), #This would be the data for the bar

            ]
        )

fig.update_layout(barmode='stack') #set the bars to stack
fig.update_traces(marker_color='red', marker_line_color='black', marker_line_width=2) #Marker_color will set the bar color, marker_line_color will set the "line" colour

fig.show()

bar
bar797×413 14.8 KB

Thanks
Payton

1 Like
3

Hi Payton,

Thanks for the response, I think this is a workaround for a regular bar chart. However, I have a floating bar chart, which indicates the minimum and maximum of my data, if I do it your way, the added bar is going to cover the minimum part of my bars.

I have a thought based on your idea, if I change the opacity of the added bar to 0, it’s gonna work well. However, when I set the opacity to 0, the line also disappear :sweat_smile:

4

I was able to find another work around, by adding another set of floating bars that have very short length – those essentially look like lines.

5

Hi @dzheng4 ,
would you mind sharing the code of your solution?

6

Sure, I’ll use Payton’s animals graph as an example.

In stead of adding the first go.bar “go.Bar(x=animals, y=[12, 14, 21],showlegend=False)”, we’ll do the following:

fig.add_trace(
    go.Bar(
        x = animals,
        y = [1, 1, 1, 1],  # Width of the "line"
        base = [12 - 1, 14 - 1, 21 - 1] ,     # Here 12,14,21 are the values of the lines we want to show for each bar.
    )
)