How to loop through the columns in data frame - r

Question

I have a following vector h=c("a","b","c","d","e")
I would like to create the dataset that looks like that using lag() function:
pr <- data.frame(your_github = h,
review_this1 = lag(h),
review_this2 = lag(h,2))
However, when I use lag the following happens:
col2=c(NA,"a","b","c","d") and col3=(NA,NA,"a","b","c")
but I need to get outcome similar to data.frame(col1=c("a","b","c","d","e"),col2=c("b","c","d","e","a"), col3=("c","d","e","a","b")) where values in col2 and col3 are looped (i.e the 2nd column is just teh 1st one that is lagged by 1, but the 1st item in 2nd is teh last item in st column).

Answer 1

Something like this?
library(dplyr)
h = c("a","b","c","d","e")
pr <- data.frame(your_github = h,
review_this1 = ifelse(is.na(lead(h)), h[1], lead(h)),
review_this2 = ifelse(is.na(lead(h, 2)), h[2:1], lead(h, 2)))
pr
# your_github review_this1 review_this2
#1 a b c
#2 b c d
#3 c d e
#4 d e a
#5 e a b

Answer 2

With base R you can achieve this with head and tail (test on tio here):
h<-letters[1:5]
pr <- data.frame(your_github = h,
review_this1 = c(tail(h, -1), head(h, -1)),
review_this2 = c(tail(h, -2), head(h, -2)))
print(pr)
Output:
your_github review_this1 review_this2
1 a b c
2 b c d
3 c d e
4 d e a
5 e a b
The idea is to take the start of the vector h with tail and concatenate it with the end of the vector taken by head minus what we got from tail so we have the same length at end for each column (vector) of the dataframe.
If you want to cycle the vector with last value becoming the first, just reverse the signs in tail and head.