"Plotly：如何在折线图中添加水平线？"

Question

I made a line graph with the code below and I'm trying to add a horizontal line at y=1. I tried following the instructions on the plotly site but it is still not showing. Does anyone know why?

date = can_tot_df.date
growth_factor = can_tot_df.growth_factor

trace0 = go.Scatter(
            x=date,
            y=growth_factor,
            mode = 'lines',
            name = 'growth_factor'
)

fig = go.Figure()
fig.add_shape(
        type='line',
        x0=date.min(),
        y0=1,
        x1=date.max(),
        y1=1,
        line=dict(
            color='Red',
        )
)


data = [trace0]
iplot(data)

Answer 1

It's hard to tell exactly what's wrong without a sample of your data. What I can tell for sure is that you're missing the arguments xref and yref to specify that the line is drawn as units of your y and x axis. Judging by your sample code, this is what you'd like to do since you're specifying your x-values in terms of dates.

Also, you don't need to worry about iplot for newer versions of plotly. You can display your chart just as easily by just running fig.show() . The figure and code sample below will show you how to use fig.show() and how to define your lines in terms of axis units.

Plot:

Code:

import plotly.graph_objects as go
import numpy as np

x = np.arange(10)

fig = go.Figure(data=go.Scatter(x=x, y=x**2))

fig.add_shape(type='line',
                x0=0,
                y0=40,
                x1=8,
                y1=40,
                line=dict(color='Red',),
                xref='x',
                yref='y'
)


fig.show()

An alternative to xref='x' is xref='paper' . Now you can specify x0 as a float between 0 and 1 spanning from the start and end of the plot.

Answer 2

df = df
fig = px.scatter(df, x="date", y="growth_factor", mode = 'lines',
      hover_name=df['growth_factor'] )

fig.update_layout(shapes=[
dict(
  type= 'line',
  yref= 'y', y0= 1, y1= 1,   # adding a horizontal line at Y = 1
  xref= 'paper', x0= 0, x1= 1
     ) 
])

fig.show()

Answer 3

You're adding the line to your fig object, but fig is not getting passed into the iplot() function, only your data . So only the trace is getting plotted.

If you're using a late version of plotly, the new syntax allows you to create this plot simply using the fig object, like:

from plotly import graph_objects as go

fig = go.Figure()

# Contrived dataset for example.
x = [1, 2, 3, 4]
y = [i**2 for i in x]

fig.add_trace(go.Scatter(
              x=x,
              y=y,
              mode = 'lines',
              name = 'growth_factor'))

fig.add_shape(type='line',
              x0=min(x),
              y0=5,
              x1=max(x),
              y1=5,
              line=dict(color='Red'))

fig.update_shapes(dict(xref='x', yref='y'))

fig.show()

Here are the plotly docs for convenience.

Answer 4

If you use subplots, then this is the easiest way I found to add an other line to a subplot. this example draws a horizontal line at y=80 for all x values

from plotly.subplots import make_subplots

fig = make_subplots(rows=2, cols=1,
                    shared_xaxes=True,
                    vertical_spacing=0.02)
[some graph]

fig.add_trace(go.Scatter(
        name='Y=80',
        x = [df['date'].min(), df['date'].max()],
        y = [80, 80],
        mode = "lines",
        marker = dict(color = 'rgba(80, 26, 80, 0.8)')
    ),row=1, col=1)

i found the solution on github :

Answer 5

You could also use fig.add_hline(y=1) --> see https://plotly.com/python/horizontal-vertical-shapes/

import plotly.graph_objects as go
import numpy as np

x = np.arange(10)

fig = go.Figure(data=go.Scatter(x=x, y=x**2))
fig.add_hline(y=40, line_width=3, line_dash="dash", line_color="green")


fig.show()