Hello!
I need help for using groupby to put values from a date-column sorted into 12 months and plot them with the median of price in those months.

This is how the dataframe looks like. Every ID has its price and I want to put the dates first into 12 groups of months. And then calculate the median of them and plot the median value into a bar chart.

please next time give the example data as a Python data structure. Also it is good if you show the code you have already written and point to the particular problems you encountered.

I created some data similar to yours. The code below does the following:

Group the data by month. Notice the grouping key provided as a lambda function.

Iterate the groups.

For each month group print the month and the median of the price.

from itertools import groupby
from statistics import median
# list of day_data tuples (date, price)
input_data = [
('2022-05-10', 70),
('2022-05-15', 72),
('2022-05-17', 79),
('2022-06-21', 80),
('2022-06-22', 81),
]
def get_year_month(date):
"""Return year and month part of an ISO 8601 date."""
return date[:7]
month_groups = groupby(input_data, lambda day_data: get_year_month(day_data[0]))
for month, month_data in month_groups:
print(month, median(day_data[1] for day_data in month_data))

output:

2022-05 72
2022-06 80.5

Now you just need to understand the program and modify it for your input data format and the desired output format and add the plotting part.