Account Number Count

I am reaching out to see if there is a way to count the number of times an account number or other key shows up in a dataframe and then place that count in the row with the account number. I know there is the value_counts() function but that is not what I am wanting to do.

This is what I am wanting to achieve. The count column is what I am wanting to append to the dataframe:

    account    count  
0   456        3
1   123        4
2   258        2
3   456        3
4   123        4
5   123        4
6   258        2
7   456        3
8   123        4

>Solution :

You can do that with either of the following.

df["count"] = df['account'].map(df['account'].value_counts())
#32ms on 1 million rows

df["count"] = df.groupby(['account'])['account'].transform('count')
#52ms on 1 million rows