Retrieve or replace a substring of a character string via the substr and substringfunctions. Additionally, these functions can be used to overwrite a part of a character string.
substr(x, start, stop)
- x – A character string.
- start – If the characters of x were numbered, then the number of the first character to be returned (or overwritten).
- stop – The number of the last character to be returned (or overwritten).
substring(x, first, last=1000000)
- x – A character string.
- first – If the characters of x were numbered, then the number of the first character to be returned (or overwritten).
- last – The number of the last character to be returned (or overwritten), which is defaulted to 1 million.
Example. Below are several simple examples of using substr. Notice in the last example of substr, where I try to extend the string out past its original length, does not work in this way. The string length cannot be changed using substr. Notice that thesubstring function has a default setting for the third argument.
> x <- "1234567890" > substr(x, 3, 3) [1] "3" > > substr(x, 5, 7) [1] "567" > > substr(x, 4, 4) <- "A" > x [1] "123A567890" > > substr(x, 2, 4) <- "TTF" > x [1] "1TTF567890" > > substr(x, 9, 12) <- "ABCD" > x [1] "1TTF5678AB" > > substring(x, 5) [1] "5678AB" > > substring(x, 5) <- "..." > x [1] "1TTF...8AB"
The substring function is a little more robust than substr.