Error when filtering pandas dataframe by column value

Question

I am having a problem with filtering a pandas dataframe. I am trying to filter a dataframe based on column values being equal to a specific list but I am getting a length error.

I tried every possible way of filtering a dataframe but got nowhere. Any help would be appreciated, thanks in advance.

Here is my code :

for ind in df_hourly.index:
    
    timeslot = df_hourly['date_parsed'][ind][0:4] # List value to filter
    filtered_df = df.loc[df['timeslot'] == timeslot]

Error : ValueError: ('Lengths must match to compare', (5696,), (4,))

Above Image : df , Below Image : df_hourly

In the above image, the dataframe I want to filter is shown. Specifically, I want to filter according to the "timeslot" column.

And the below image shows the the dataframe which includes the value I want to filter by. I specifically want to filter by "date_parsed" column. In the first line of my code, I iterate through every row in this dataframe and assign the first 4 elements of the list value in df_hourly["date_parsed"] to a variable and later in the code, I try to filter the above dataframe by that variable.

Answer 1

When comparing columns using ==, pandas try to compare value by value - aka does the first item equals to first item, second item to the second and so on. This is why you receive this error - pandas expects to have two columns of the same shape.

If you want to compare if value is inside a list, you can use the .isin (documentation):

df.loc[df['timeslot'].isin(timeslot)]

Depends on what timeslot is exactly, you might to take timeslot.values or something like that (hard to understand exactly without giving an example for your dataframe)