In R, iterating over two datasets and getting back results without looping - r

Question

I have two data sets, Transaction_long, and Transaction_short. Transaction_long has many quotes of policy and price with a purchase point (denoted by true) in the dataset. Transaction_short has only entries of the purchase points.
My objective is to add a column in the Transaction_short dataset called Policy_Change_Frequency. For every customer in the short dataset, iterate over the rows for that customer in the long dataset and calculate how many time the policy changed.
To find the policy change I can use sum(diff(Transaction_Long$policy)!=0) but not sure how to iterate over these two data sets and get results
Details:
Customer_Name : name of customer
Customer_ID: Customer Identifier number
Purchase: Boolean variable (Yes-1,No-0)
Policy: Categorical (takes values 1-5)
Price : Price quoted
Data set1-Transaction_Long
Customer_Name,Customer_ID,Purchased,Policy,Price
Joe,101,0,1,500
Joe,101,0,1,505
Joe,101,0,2,510
Joe,101,0,2,504
Joe,101,0,2,507
Joe,101,0,1,505
Joe,101,1,3,501
Mary,103,0,1,675
Mary,103,0,3,650
Mary,103,0,2,620
Mary,103,0,2,624
Mary,103,0,2,630
Mary,103,1,2,627
Data set 2:Transaction_Short
Customer_Name , Customer_ID,Purchased,Policy, Price
Joe,101,1,3,501
Mary,103,1,2,627
Need to add a Policy Change Frequency column in the Transaction Short Dataset, so my final Transcation short Dataset will look like
Final Dataset should look like this
Customer_Name , Customer_ID,Purchased, Policy, Price,Policy_ChangeFreq
Joe,101,1,3,501,3
Mary,103,1,2,627,2

Answer 1

Consider a calculated column for policy change which tags changes from previous row within each customer with one. Then, aggregates the ones for a count. Merge is used due to two aggregations needed (final row for each customer and PolicyChanged count):
Transaction_Long$PolicyChangedFreq <- sapply(1:nrow(Transaction_Long),
function(i)
if (i > 1) {
ifelse(Transaction_Long$Policy[i-1]==
Transaction_Long$Policy[i], 0,
ifelse(Transaction_Long$Customer_ID[i-1] !=
Transaction_Long$Customer_ID[i], 0, 1))
} else { 0 }
)
Transaction_Final <- merge(aggregate(.~ Customer_ID + Customer_Name,
Transaction_Long[,c(1:5)], FUN = tail, n = 1),
aggregate(.~ Customer_ID + Customer_Name,
Transaction_Long[,c(1:2,6)], FUN = sum),
by = c('Customer_ID', 'Customer_Name'))
Transaction_Final
# Customer_ID Customer_Name Purchased Policy Price PolicyChangedFreq
#1 101 Joe 1 3 501 3
#2 103 Mary 1 2 627 2

Answer 2

#Parfait. Thank you for the solution. i solved this using the sqldf package in R
for (i in 1:nrow(Transaction_short)){
sql <- sprintf("SELECT policy from Transaction_long where customer_ID = %s",ML_Train_short$customer_ID[i])
df<- sqldf(sql)
NF <- sum(df$policy[-1]!= df$policy[-length(df$policy)])
ML_Train_short$Policy_Change_Freq[i] <- NF
}
Since i have about 500K rows in the long dataset and about 100K in the short dataset..this is taking a while..is there any other solution that does not require loops? Thank you