# Import libraries
import pandas as pd
import numpy as np

# Create sample dataframe
df = pd.DataFrame({'a': ['A1', 'A1', 'A2', 'A3', 'A4', 'A3'],
                   'value': [1,2,3,4,5,6]})

# Calculate count, mean
temp1 = df.groupby(['a']).count().reset_index().rename(columns={'value':'count'})
temp2 = df.groupby(['a'])['value'].mean().reset_index().rename(columns={'value':'mean'})

# Add columns to existing dataframe
df.merge(temp1, on='a', how='inner').merge(temp2, on='a', how='inner')

# Add columns to a new dataframe
df2 = temp1.merge(temp2, on='a', how='inner')
df2