How to Reverse the delimited parts of a string

Question

I'm trying to reverse the parts of a hierarchical name found in a dataframe so that I can work with the string for the reverse path. Here is what I did:

flip <- function(x) {                      # My attempted function
  str <- str_split(x,":",simplify=TRUE)
  paste(str[length(str):1], collapse = ":")
}

Data <- data.frame(                        # The data
  X = c("one:two:three:four","five:six:seven:eight")
)

mutate(Data,                               # My attempt & result
   Xflip = flip(X)
)
#>                     X                Xflip
#>1   one:two:three:four eight:four:seven:three:six:two:five:one
#>2 five:six:seven:eight eight:four:seven:three:six:two:five:one


# What I am looking for
#>                     X                Xflip
#>1   one:two:three:four   four:three:two:one
#>2 five:six:seven:eight eight:seven:six:five

Thank you!

My apologies -- there are some typos in my example above. I will edit my example. Thanks for response so far. — A. Maffei, Mar 06 '18 at 22:58
It's not clear to me that this is an exact duplicate as I need to reverse the parts of a delimited string rather than each character in the string. I've edited the title to reflect this difference. I note that in the "How to reverse a string in R" article a strsplit is performed but employs NULL as delimiter - not sure why. — A. Maffei, Mar 12 '18 at 00:31

Maurits Evers · Answer 1 · 2018-03-06T23:14:57.347

1

Or using stringr::str_split_fixed:

df$Xflip <- apply(stringr::str_split_fixed(df$X, ":", 4), 1, function(x) 
    paste0(rev(x), collapse = ":"))
#                     X                Xflip
#1   one:two:three:four   four:three:two:one
#2 five:six:seven:eight eight:seven:six:five

Or using stringr::str_split:

df$Xflip <- sapply(stringr::str_split(df$X, ":"), function(x) 
    paste0(rev(x), collapse = ":"));

You can do the same using transform:

transform(df, Xflip = sapply(stringr::str_split(X, ":"), function(x) 
    paste0(rev(x), collapse = ":")))

The stringr::str_split method will also work if X contains a varying number of ":" separated entries.

edited Mar 06 '18 at 23:14

answered Mar 06 '18 at 23:05

Maurits Evers

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Thanks for your help. I've obviously got more to learn about R programming. You've inspired me to "dig in" a bit more. – A. Maffei Mar 12 '18 at 00:34
No worries @A.Maffei; glad I could help. Please consider upvoting if the answer was useful. – Maurits Evers Mar 12 '18 at 04:15

score 0 · Accepted Answer · answered Mar 06 '18 at 22:51

I'd split, flip, then concatenate. But there might be an easier way using mutate :)

flipper <- function(x){

    splitVector <- unlist(strsplit(x, ":")) #Split it by ":"
    flipVector <- rev(splitVector ) #Reverse it
    flipString <- paste0(flipVector, collapse = ":") #Paste it back together!
    return(flipString)

}

That should do the job for you!

Data$Xflip <- sapply(as.character(Data$X), flipper)

How to Reverse the delimited parts of a string

2 Answers2