How to create a loop that changes part of a column name in a data frame - r

Question

I am trying to find Cronbach's Alpha for survey data containing a series of multi-item measures. Rather than have to manually write out every single multi-item measure, it looks like something a loop should be able to manage far more effectively, but it needs to change only part of the column name, according to the question number.
The basic idea as it currently sits in my head would be...
for (N in 4:22) {
ytqN <- data.frame(YT_Data$QNa, YT_Data$QNb, YT_Data$QNc)
alpha(ytqN)
}
The loop would then create new data frames for each multi item measure and run Cronbach's Alpha as it goes.
This doesn't work though. :(
ytq4 <- data.frame(YT_Data$Q4a, YT_Data$Q4b, YT_Data$Q4c)
alpha(ytq4)
ytq5 <- data.frame(YT_Data$Q5a, YT_Data$Q5b, YT_Data$Q5c)
alpha(ytq5)
ytq6 <- data.frame(YT_Data$Q6a, YT_Data$Q6b, YT_Data$Q6c)
alpha(ytq6)
ytq7 <- data.frame(YT_Data$Q7a, YT_Data$Q7b, YT_Data$Q7c)
alpha(ytq7)
ytq8 <- data.frame(YT_Data$Q8a, YT_Data$Q8b, YT_Data$Q8c)
alpha(ytq8)
ytq9 <- data.frame(YT_Data$Q9a, YT_Data$Q9b, YT_Data$Q9c)
alpha(ytq9)
ytq10 <- data.frame(YT_Data$Q10a, YT_Data$Q10b, YT_Data$Q10c)
alpha(ytq10)
ytq11 <- data.frame(YT_Data$Q11a, YT_Data$Q11b, YT_Data$Q11c)
alpha(ytq11)
ytq12 <- data.frame(YT_Data$Q12a, YT_Data$Q12b, YT_Data$Q12c)
alpha(ytq12)
ytq13 <- data.frame(YT_Data$Q13a, YT_Data$Q13b, YT_Data$Q13c)
alpha(ytq13)
ytq14 <- data.frame(YT_Data$Q14a, YT_Data$Q14b, YT_Data$Q14c)
alpha(ytq14)
ytq15 <- data.frame(YT_Data$Q15a, YT_Data$Q15b, YT_Data$Q15c)
alpha(ytq15)
ytq16 <- data.frame(YT_Data$Q16a, YT_Data$Q16b, YT_Data$Q16c)
alpha(ytq16)
ytq17 <- data.frame(YT_Data$Q17a, YT_Data$Q17b, YT_Data$Q17c)
alpha(ytq17)
ytq18 <- data.frame(YT_Data$Q18a, YT_Data$Q18b, YT_Data$Q18c)
alpha(ytq18)
ytq19 <- data.frame(8 - YT_Data$Q19a, YT_Data$Q19b, YT_Data$Q19c)
# Reverse code Q19a
alpha(ytq19)
ytq20 <- data.frame(YT_Data$Q20a, YT_Data$Q20b, YT_Data$Q20c)
alpha(ytq20)
ytq21 <- data.frame(YT_Data$Q21a, YT_Data$Q21b, YT_Data$Q21c)
alpha(ytq21)
ytq22 <- data.frame(YT_Data$Q22a, YT_Data$Q22b, YT_Data$Q22c)
alpha(ytq22)
The desired results would be a single output containing all the Cronbach's Alphas for the multi item measures for questions 4-22 in the data set I am currently working on executed via a single piece of code, rather than have to go question by question.

Answer 1

It's easier to help if you include your data, but I guess this should work:
alpha_list = list()
for(N in 4:22){
ytq = data.frame(YT_Data[paste0("Q",N,"a")],
YT_Data[paste0("Q",N,"b")],
YT_Data[paste0("Q",N,"c")])
alpha_list[[N]] = alpha(ytq)
}
We are using paste0() to create the column names while looping on N. alpha_list will be a list with the results given by alpha()