Plotly: How to set custom xticks

Question

From plotly doc:

layout > xaxis > tickvals:

Sets the values at which ticks on this axis appear. Only has an effect if tickmode is set to "array". Used with ticktext.

layout > xaxis > ticktext:

Sets the text displayed at the ticks position via tickvals. Only has an effect if tickmode is set to "array". Used with tickvals.

Example:

import pandas as pd
import numpy as np

np.random.seed(42)
feature = pd.DataFrame({'ds': pd.date_range('20200101', periods=100*24, freq='H'), 
                        'y': np.random.randint(0,20, 100*24) , 
                        'yhat': np.random.randint(0,20, 100*24) , 
                        'price': np.random.choice([6600, 7000, 5500, 7800], 100*24)})


import plotly.graph_objects as go
import plotly.offline as py
import plotly.express as px
from plotly.offline import init_notebook_mode

init_notebook_mode(connected=True)


y = feature.set_index('ds').resample('D')['y'].sum()

fig = go.Figure()
fig.add_trace(go.Scatter(x=y.index, y=y))


x_dates = y.index.to_series().dt.strftime('%Y-%m-%d').sort_values().unique()


layout = dict(
    xaxis=dict(
        tickmode="array",
        tickvals=np.arange(0, x_dates.shape[0],2).astype(int),
        ticktext=x_dates[::2],
        tickformat='%Y-%m-%d',
        tickangle=45,
    )
)

fig.update_layout(layout)
fig.show()

Result:

Since length of x_dates[::2] is 50 , the ticknumber doesn't match at all . How do I sovle it ??

Answer 1

I normally use the approach below. You should know that tickvals is to be regarded as a positional argument and works best (perhaps only) with numerical values and not dates. Use ticktext to display the dates in your preferred format.

Snippet 1:

fig.update_xaxes(tickangle=45,
                 tickmode = 'array',
                 tickvals = df_tips['date'][0::40],
                 ticktext= [d.strftime('%Y-%m-%d') for d in datelist])

Plot 1:

Now you can change tickvals=np.arange(0, y.shape[0]).astype(int)[0::40] to tickvals=np.arange(0, y.shape[0]).astype(int)[0::80] and get:

Plot 2:

So why didn't this work for you the first time? A number of reasons:

1. Your resampled pandas series y had dates as indexes, so y.index were set as x-axis values.
2. y.index returns dates
3. When you set the tickmark positions through fig.update_xaxes(tickvals), this works better with integer values.

And what did I do to fix it?

1. I reset the index after resampling so that y.index does not return dates.
2. Changed y to a dataframe using .to_frame.
3. Changed to fig.add_trace(go.Scatter(x=y.index, y=y.y)) which otherwise would have failed since this is now a dataframe and not a series.
4. Your dates are now retrieved as x_dates = y.ds

I know y=y.y looks really weird, but I just left it like that as a friendly reminder to give your pandas series or dataframes more sensible names than a single letter like y that's more likely to be confused with a single, index-free, array or list.

Complete code:

import pandas as pd
import numpy as np
import plotly.graph_objects as go
import plotly.offline as py
import plotly.express as px
from plotly.offline import init_notebook_mode

# data
np.random.seed(42)
feature = pd.DataFrame({'ds': pd.date_range('20200101', periods=100*24, freq='H'), 
                        'y': np.random.randint(0,20, 100*24) , 
                        'yhat': np.random.randint(0,20, 100*24) , 
                        'price': np.random.choice([6600, 7000, 5500, 7800], 100*24)})

# resampling
y = feature.set_index('ds').resample('D')['y'].sum()#.to_frame()
y=y.to_frame()
y.reset_index(inplace=True)

# plotly setup
fig = go.Figure()
fig.add_trace(go.Scatter(x=y.index, y=y.y))

# x-ticks preparations
x_dates = y.ds
tickvals=np.arange(0, y.shape[0]).astype(int)[0::40]
ticktext=x_dates

# update tickmarks
fig.update_xaxes(tickangle=45,
                 tickmode = 'array',
                 tickvals = tickvals,
                 ticktext=[d.strftime('%Y-%m-%d') for d in ticktext])

fig.show()