The functions `head` and `tail` are very useful for working with lists, tables, data frames and even functions.

But they do not work on strings. It is easy to define such functions

> strtail <- function(s,n=1) {

+ if(n<0)

+ substring(s,1-n)

+ else

+ substring(s,nchar(s)-n+1)

+ }

> strhead <- function(s,n) {

+ if(n<0)

+ substr(s,1,nchar(s)+n)

+ else

+ substr(s,1,n)

+ }

and start using them:

> strhead("abc", 1)

[1] "a"

> strhead("abc", -1)

[1] "ab"

> strtail("abc", 1)

[1] "c"

> strtail("abc", -1)

[1] "bc"

It is not a good idea to name these functions `head.character` and `tail.character` because this

has unexpected effects if applied to a vector of strings.

Other useful string functions are defined in the the

stringr package.

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