Zero occurrences/frequency using value_counts() in PANDAS

Question

I have a table containing dates and the various cars sold on each dates in the following format (These are only 2 of many columns):

DATE       CAR
2012/01/01         


        

Answer 1

The default behavior of type category is exactly what you want. The non present categories will display with a value of zero. You just need to do:

df.astype({'CAR': 'category'})[df.CAR=='BMW']['DATE'].value_counts()

or better yet, make it definitively a category in your dataframe:

df.CAR = df.CAR.astype('category')
df[df.CAR=='BMW'].DATE.value_counts()

The category type is a better representation of your data and more space-efficient.