g5_adding_label.py

#create a dataframe with customer id and first purchase date in tx_next
tx_next_first_purchase = tx_next.groupby('CustomerID').InvoiceDate.min().reset_index()
tx_next_first_purchase.columns = ['CustomerID','MinPurchaseDate']

#create a dataframe with customer id and last purchase date in tx_6m
tx_last_purchase = tx_6m.groupby('CustomerID').InvoiceDate.max().reset_index()
tx_last_purchase.columns = ['CustomerID','MaxPurchaseDate']

#merge two dataframes
tx_purchase_dates = pd.merge(tx_last_purchase,tx_next_first_purchase,on='CustomerID',how='left')

#calculate the time difference in days:
tx_purchase_dates['NextPurchaseDay'] = (tx_purchase_dates['MinPurchaseDate'] - tx_purchase_dates['MaxPurchaseDate']).dt.days

#merge with tx_user 
tx_user = pd.merge(tx_user, tx_purchase_dates[['CustomerID','NextPurchaseDay']],on='CustomerID',how='left')

#print tx_user
tx_user.head()

#fill NA values with 999
tx_user = tx_user.fillna(999)