Is there a way to prevent the legend on plotly from moving up into the chart when its orientation is horizontal?

Question

Context

I am currently in the middle of creating a data visualisation web app. I am using Plotly to create a timeseries. I am having trouble with the legend.

I want the legend to remain at the bottom as the labels of the data are quite long and so interfere with the overall dimensions of the data. I chose the orientation to be horizontal.

But as I add more data, the legend moves up rather than remain in a fixed position so that the new data can be added going down. Instead the whole legend goes up as new data is added to the chart.

My code is below:

plotly_fig = px.line(data_frame=dataframe_cols1,x=dataframe_cols1.index,y=Columns_select1,
                            width=780, height=730) # Get data from the dataframe with selected columns, choose the x axis as the index of the dataframe, y axis is the data that will be multiselected
        
        # Legend settings
        plotly_fig.update_layout(showlegend=True)       
        plotly_fig.update_layout(legend=dict(
                          orientation = "h",
                          yanchor="bottom",
                          y=-.50,
                          xanchor="right",
                          x=1
                        ))    

Problem

How can I prevent the legend from moving up as I add new data? In other words, how can I fix the legend in its position to prevent it from 'mingling' with the chart?

Answer 1

There's really only one way; make room and adjust legend position.

And in this case you would do that through:

1. fig.update_layout(height=1000)
2. fig.update_layout(margin=dict(l=20, r=20, t=20, b=20)
3. fig.update_layout(legend=dict(orientation = "h", yanchor="bottom",y=-1.1,xanchor="left", x=0))

Sample plot

Complete code:

import pandas as pd
import numpy as np
import plotly
import plotly.express as px

# data
start = 2021
ncols = 20
nrows = 1000
cols = [str(i) for i in np.arange(start, start+ncols)]
df = pd.DataFrame(np.random.randint(-1,2, (nrows,ncols)), columns = cols).cumsum()
df.iloc[0] = 0

# figure
fig = px.line(df, x=df.index, y=cols,width=780, height=730)

# updating names
fig.for_each_trace(lambda t: t.update(name=t.name + ' Very lengthy name to reproduce the challenge') )
    
# legend position
fig.update_layout(showlegend=True) 
fig.update_layout(legend=dict(
                  orientation = "h",
                  yanchor="bottom",
                  y=-1.1,
                  xanchor="left",
                  x=0)) 

height = 1000
fig.update_layout(
    autosize=False,
    width=750,
    height=height)

fig.update_layout(
    margin=dict(l=20, r=20, t=20, b=20),
    paper_bgcolor="LightSteelBlue")

# plotly.offline.plot(fig, filename='C:/plotlyplots/lifeExp.html')
fig.show()