r - Get the first and last letter in alphabetic order for a character vector -

i doing r exercise:

write function splits string letters , return min & max letters according alphabetical order.

here's vector:

cities <- c("new york", "paris", "london", "tokyo", "rio de janeiro", "cape town") 

here's code have written:

first_and_last <- function(name){   name <- gsub (" ", "", name)   letters <- strsplit(name, split = "")   c(first = min(letters), last = max(letters))    } 

however, got errors when run it:

first_and_last(cities) #error in min(letters) (from #4) : invalid 'type' (list) of argument 

kindly let me know what's missing in code? thanks!

i assuming want element-wise operation, i.e., each element of cities, extract first , last letter in alphabetic order. need:

first_and_last <- function(name){   name <- gsub (" ", "", name)   myname <- strsplit(name, split = "")   result <- t(sapply(myname, range))  ## use function `range`   rownames(result) <- name   colnames(result) <- c("first", "last")   return(result)   }  first_and_last(cities)  #                first last # new york       "e"   "y"  # paris          "a"   "s"  # london         "d"   "o"  # tokyo          "k"   "y"  # rio de janeiro "a"   "r"  # cape town      "a"   "w"  

i have used function range(). return min , max. r's built-in implementation function(x) c(min(x), max(x)).

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follow-up

thanks, problem solved. i'm taking online course in r. in solution, used following line of code. if possible please explain, line of code mean. especially, double bracket part "[[1]]": letters <- strsplit(name, split = "")[[1]]

strsplit returns list. let's try:

strsplit("bath", split = "") #[[1]] #[1] "b" "a" "t" "h" 

if want access character vector, need [[1]]:

strsplit("bath", split = "")[[1]] #[1] "b" "a" "t" "h" 

only vector can take min / max. example:

min(strsplit("bath",split="")) #error in min(strsplit("bath", split = "")) :  #  invalid 'type' (list) of argument  min(strsplit("bath",split="")[[1]]) #[1] "a" 

i believe online example see takes single character. if have vector input like:

strsplit(c("bath", "bristol", "cambridge"), split = "") #[[1]] #[1] "b" "a" "t" "h"  #[[2]] #[1] "b" "r" "i" "s" "t" "o" "l"  #[[3]] #[1] "c" "a" "m" "b" "r" "i" "d" "g" "e" 

and want apply range each list element, sapply handy:

sapply(strsplit(c("bath", "bristol", "cambridge"), split = ""), range) #     [,1] [,2] [,3] #[1,] "a"  "b"  "a"  #[2,] "t"  "t"  "r"  

my function first_and_last above based on sapply. yet nice presentation, have transposed result , given row / column names.

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gosh, realize sked question on [[]] 2 days ago: double bracket [[]] within function. why still asking me explanation???