pyplot line plotting erratically

Question

I got these 2 simple csv data but when plotting the 'mon' line gone strange toward the end. When plotting one chart, it is fine but when the 2 charts plotted together the 'monarch' one goes strange.

Thanks in advance.

Here is the code

import pandas as pd 
from matplotlib import pyplot as plt

def run_plot1():
    df_ash = pd.read_csv('./data/ashburn.csv')
    df_mon = pd.read_csv('./data/monarch1bed.csv')

    plt.grid(True)

    plt.plot(df_ash['Date'], df_ash['Ash1bed'], label='Ashburn 1 bed')
    plt.plot(df_mon['Date'], df_mon['Mon1bed'], label='Monarch 1 bed')


    plt.xlabel("Date")
    plt.ylabel("Rate")

    plt.style.use("fivethirtyeight")
    plt.title("One Bed Comparison")
    plt.legend()
    plt.savefig('data/sample.png')
    plt.tight_layout()

    plt.show()

run_plot1()

and the csv datas:

Date,Ash1bed,Ash2bed,Ash3bed
08-01,306,402
22-01,181,286,349
05-02,176,281,336
19-02,188,293,369
04-03,201,306,402
18-03,209
01-04,217,394,492
15-04,209,354,455
29-04,197,302,387
13-05,205,326,414
27-05,217,362,473
10-06,390,532
08-07,415
22-07,415
05-08,415
19-08,415
15-09,290,452,594

and another :

Date,Mon1bed
08-01,230
05-02,160
19-02,160
04-03,190
18-03,190
01-04,260
15-04,260
29-04,260
13-05,300
27-05,330
10-06,330
24-06,350
08-07,350
22-07,350
05-08,350
19-08,350
02-09,350

If you have Date in the format YYYY-MM-DD and convert it to datetime you should have a nice plot. — rpanai
– rpanai, Commented Jan 2, 2020 at 17:56

Valdi_Bo · Accepted Answer · 2020-01-02 18:37:14Z

The basic reason of erratic printout is that your Date columns in both DataFrames are of string type.

Convert them to datetime:

df_ash.Date = pd.to_datetime(df_ash.Date, format='%d-%m')
df_mon.Date = pd.to_datetime(df_mon.Date, format='%d-%m')

But to have "reader friendly" X-axis labels, a number of additional steps are required.

Start from necessary imports:

from pandas.plotting import register_matplotlib_converters
import matplotlib.dates as mdates

Then register matplotlib converters:

register_matplotlib_converters()

And to get proper printout, run:

fig, ax = plt.subplots()  # figsize=(10, 6)
ax.grid(True)
ax.plot(df_ash['Date'], df_ash['Ash1bed'], label='Ashburn 1 bed')
ax.plot(df_mon['Date'], df_mon['Mon1bed'], label='Monarch 1 bed')
plt.xlabel("Date")
plt.ylabel("Rate")
plt.style.use("fivethirtyeight")
plt.title("One Bed Comparison")
plt.legend()
dm_fmt = mdates.DateFormatter('%d-%m')
ax.xaxis.set_major_formatter(dm_fmt)
plt.xticks(rotation=45);

For your data I got:

Roshan Santhosh · Accepted Answer · 2020-01-02 17:59:47Z

0

You should convert the date variable to a date format

df1.Date = pd.to_datetime(df1.Date, format='%d-%m')

df2.Date = pd.to_datetime(df2.Date, format='%d-%m')

plt.plot(df1.Date, df1.Ash1bed)
plt.plot(df2.Date, df2.Mon1bed)

answered Jan 2, 2020 at 17:59

Roshan Santhosh

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