How to add a column containing the occcurence of every element in pandas?-CodePudding

Given a DataFrame such as

import pandas as pd
df = pd.DataFrame({'a': [700, 700, 600, 600, 600]}

How can I extend it with a column containing the occurrence for each row? Such that it ends up as

df_ext = pd.DataFrame({
    'a':          [700, 700, 600, 600, 600],
    'Occurrence': [  2,   2,   3,   3,   3]
})

Adding the column is not so much of a problem, rather how to get the occurrence list.

CodePudding user response：

You can transform groupby_count:

df['Occurrences'] = df.groupby('a')['a'].transform('count')

or you can map value_counts on "a":

df['Occurrences'] = df['a'].map(df['a'].value_counts())

Output:

     a  Occurrences
0  700            2
1  700            2
2  600            3
3  600            3
4  600            3

CodePudding user response：

df['occurance']=df['a'].map(df.groupby('a').agg('size'))

CodePudding user response：

Simply use:

df['b'] = df['a'].apply(lambda x: list(df['a']).count(x))