Reduce the number of xticks in matplotlib dynamically while plotting data of prices vs time

Question

My python matplotlib script:

plt.plot(graphdf["Price"],color='red')
plt.xticks(rotation=90)

Need help in reducing the number of ticks dynamically, my program scrapes data continuously and while plotting it the x-axis becomes jumbled after some time, like after some 40 xtick labels.

(I don't have fixed number of data points, it keeps growing each time my program scrapes additional data For example: at 9:37 I'll have just 3 data points, at 9:45 I'll have 5 datapoints etc. Iam plotting it in the below graph continuously)

I have a simple dataset which has price vs Time (stock market prices) like this:

My graph is like this

Answer 1

Option 1: x axis datetime type

Answer

I suppose your data are in a file named data.csv. If you load it with pd.read_csv, you need to pay attention to the format of the 'Time' column. Look at the output of:

print(graphdf.info())

If the DType of the column 'Time' is object, pandas identifies the values of this column as str. In this case, you need to convert them to datetime with:

graphdf['Time'] = pd.to_datetime(graphdf['Time'], format = '%H:%M')

Finally you can set the format of the labels you see on the x axis with:

ax.xaxis.set_major_formatter(md.DateFormatter('%H:%M'))

Check this answer for reference.

---

Whole code

import pandas as pd
import matplotlib.pyplot as plt
import matplotlib.dates as md

graphdf = pd.read_csv('data.csv')
graphdf['Time'] = pd.to_datetime(graphdf['Time'], format = '%H:%M')

fig, ax = plt.subplots()

ax.plot(graphdf['Time'],graphdf['Price'],color='red')
plt.xticks(rotation=90)
ax.xaxis.set_major_formatter(md.DateFormatter('%H:%M'))

plt.show()

---

Plot

---

Option 2: x axis str type

Answer

In the case you do not want x axis as a general time %H:%M axis, but you want to keep your original ticks, you have to mantain the x axis as a str type and simply sample original ticks, then apply them to the axis:

xticks = graphdf['Time'][::2]
ax.set_xticks(xticks)

You can slice original ticks with [::n], where n is the step. If n = 2 you pick alternative ticks; if n = 3 you pick a tick every 3 and so on.

Whole code

import pandas as pd
import matplotlib.pyplot as plt

graphdf = pd.read_csv('data.csv')

fig, ax = plt.subplots()

ax.plot(graphdf['Time'],graphdf['Price'],color='red')
plt.xticks(rotation=90)
xticks = graphdf['Time'][::2]
ax.set_xticks(xticks)

plt.show()

---

Plot