hwo to write crosstab query in python?

i have a function in python that use crosstab on dataframe

def event_mouhafaza(self,df):
        df_event_mohafazat_crosstab = pd.crosstab(df['event_mohafaza'],df['event_type'])
        print(df_event_mohafazat_crosstab)

the above function work as it should and return the expected result.

when i try to replace the values of the crosstab query by variables the system crash.

def event_mouhafaza(self,df,items):
   
     for item in items:
         item1 = items[0]
         item2 = items[1]
        
     df = df.set_index(item2)    
     df_event_mohafazat_crosstab = pd.crosstab(df,item1,item2)
     print(df_event_mohafazat_crosstab)

And display this error:

df_event_mohafazat_crosstab = pd.crosstab(df,item1,item2)
  File "F:\AIenv\lib\site-packages\pandas\core\reshape\pivot.py", line 577, in crosstab
    raise ValueError("values cannot be used without an aggfunc.")
ValueError: values cannot be used without an aggfunc.

where is the error in the second function and how to fix it?

Solution

You're using the crosstab function wrong in the second example. pd.crosstab does not take a dataframe as its first argument. Right now you're calling the function like this (using kwargs to highlight the issue). When you specify the values argument (like you are with a positional argument), pandas also expects something to be passed into the aggfunc argument as well. See the documentation for more info on that.

# This will error out.
pd.crosstab(index=df, columns=item1, values=item2)

If item1 and item2 are the names of columns within your dataframe, you'll need to do this:

pd.crosstab(index=df[item1], columns=df[item2])

Next, you don't actually want to set item2 as the index if you're planning to use it in the crosstabulation. And your for-loop isn't actually doing anything, you can assign item1 and item2 without it:

def event_mouhafaza(self,df,items):
   
     item1 = items[0]
     item2 = items[1]
        
     df_event_mohafazat_crosstab = pd.crosstab(index=df[item1], columns=df[item2])
     print(df_event_mohafazat_crosstab)