[Python] Average numeric columns and return single string for string columns using pandas...

I have a dataframe that looks like the following:

ID Type Size
0 123 Red 5
1 456 Blue 7
2 789 Yellow 12
3 789 Yellow 4


I now want to aggregate by ID and take the mean of the size for duplicates. However, I wish to only return the same string for Type, not concatenate it. I have attempted to capture this using agg:

df = pd.DataFrame({'ID' : [123, 456, 789, 789], 'Type' : ['Red', 'Blue', 'Yellow', 'Yellow'], 'Size' : [5, 7, 12, 4]})

def identity(x):
return x

special_columns = ['Type']
aggfuncs = {col: statistics.mean for col in df.columns}
aggfuncs.update({col:identity for col in special_columns})
df.groupby(['ID'], as_index=False).agg(aggfuncs)


However, this still turns into an array of the repeated string:

ID Type Size
0 123 Red 5
1 456 Blue 7
2 789 [Yellow, Yellow] 8


The end result I wanted was:

ID Type Size
0 123 Red 5
1 456 Blue 7
2 789 Yellow 8


How can this be achieved?

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