Python, Pandas: Use MC method to keep random subset of records within different values of the primary key

df_sample_within_pkey.py

df_out = pd.DataFrame(columns=df.columns)
df_temp = pd.DataFrame(columns=df.columns)
for elem in a_list:
    df_temp =  df[df.pkey==elem]
    if len(df_temp) > a_number:
        df_temp_ind = df_temp.index.map(lambda x: x if np.random.binomial(1, prob_keep)==1 else None)
        df_temp = df_temp.loc[df_temp_ind,].dropna()
    else:
        pass
    df_out = df_out.append(df_temp, ignore_index=True)