Python to add data label on linechart from Matplotlib and Pandas GroupBy

I am hoping to add data labels to a line chart produced by Matplotlib from Pandas GroupBy.

import matplotlib.pyplot as plt
import pandas as pd
from io import StringIO

csvfile = StringIO(
"""
Name	Year - Month	Score
Mike	2022-09	192
Mike	2022-08	708
Mike	2022-07	140
Mike	2022-05	144
Mike	2022-04	60
Mike	2022-03	108
Kate	2022-07	19850
Kate	2022-06	19105
Kate	2022-05	23740
Kate	2022-04	19780
Kate	2022-03	15495
Peter	2022-08	51
Peter	2022-07	39
Peter	2022-06	49
Peter	2022-05	49
Peter	2022-04	79
Peter	2022-03	13
Lily	2022-11	2
David	2022-11	3
David	2022-10	6
David	2022-08	2""")

df = pd.read_csv(csvfile, sep = '\t', engine='python')

for group_name, sub_frame in df.groupby("Name"):
	if sub_frame.shape[0] >= 2:
    	sub_frame_sorted = sub_frame.sort_values('Year - Month')       # sort the data-frame by a column

	    line_chart = sub_frame_sorted.plot("Year - Month", "Score")

		label = sub_frame_sorted['Score']
    	line_chart.annotate(label, (sub_frame_sorted['Year - Month'], sub_frame_sorted['Score']), ha='center') 

plt.show()

The 2 lines for data labels throw an error:

ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

How can I have them corrected?

So, the problem should be inside your for loop.

You can replace your code by this one:

for group_name, sub_frame in df.groupby("Name"):
    if sub_frame.shape[0] >= 2:
        sub_frame_sorted = sub_frame.sort_values('Year - Month')

        line_chart = sub_frame_sorted.plot("Year - Month", "Score")
        for x, y in zip(sub_frame_sorted["Year - Month"], sub_frame_sorted["Score"]):
            label = "{:.0f}".format(y)  # format the label as a string
            line_chart.annotate(label, (x, y), textcoords="offset points", xytext=(0,10), ha='center') 

And also if you face error regarding 'Year-Month' you should convert that using to_datetime() method.

Please let me know if this helps. Thanks.

As the error says that the problem is in the annotate(). The sub_frame_sorted is a dataframe and you need to use a for loop to get each of the items within it before using annotate. Also, the x-axis is year-month, which is seen as string and you will run into issues. So, you need to just use index. I have used 0,1,2... using i. This should work... you can add a small offset if you think the text is overlapping a line
Hope this is what you are looking for.

Updated code

for group_name, sub_frame in df.groupby("Name"):
    if sub_frame.shape[0] >= 2:
        sub_frame_sorted = sub_frame.sort_values('Year - Month')       # sort the data-frame by a column
        line_chart = sub_frame_sorted.plot("Year - Month", "Score", legend=False)
        i=0
        for ix, vl in sub_frame_sorted.iterrows(): 
            line_chart.annotate(vl['Score'], (i, vl['Score']), ha='center') 
            i=i+1
plt.show()

Output plots