Subtracting dates in Python for Gantt chart-CodePudding

I am following a tutorial to make a Gantt chart with this tutorial: https://towardsdatascience.com/gantt-charts-with-pythons-matplotlib-395b7af72d72

I have tried to recreate part of the test dataset with the following script:

import pandas as pd   

data = [['TSK M', 'IT', '2022-03-17',  '2022-03-20', '0.0'], ['TSK N', 'MKT', '2022-03-17', '2022-03-19',  '0.0']]    

df = pd.DataFrame(data, columns = ['Task', 'Department',  'Start', 'End', 'Completion'])

Then processing the dataframe through the first part of the tutorial, I end up with and error message:

proj_start = df['Start'].min()

df['start_num'] = (df.Start-proj_start).dt.days

TypeError: unsupported operand type(s) for -: 'str' and 'str'

I have tried to convert the data in integer with the function int(), but the error persist. Would anyone know what is wrong here?

CodePudding user response：

You need to convert date column to datetime type first

df['Start'] = pd.to_datetime(df['Start'])
df['End'] = pd.to_datetime(df['End'])

# Or

df[['Start', 'End']] = df[['Start', 'End']].apply(pd.to_datetime)