how to add a character to a string in R [duplicate] - r

Question

This question already has answers here:
Insert a character at a specific location in a string
(8 answers)
Closed 6 years ago.
I have something like this:
text <- "abcdefg"
and I want something like this:
"abcde.fg"
how could I achieve this without assigning a new string to the vector text but instead changing the element of the vector itself? Finally, I would like to randomly insert the dot and actually not a dot but the character element of a vector.

Answer 1

We can try with sub to capture the first 5 characters as a group ((.{5})) followed by one or more characters in another capture group ((.*)) and then replace with the backreference of first group (\\1) followed by a . followed by second backreference (\\2).
sub("(.{5})(.*)", "\\1.\\2", text)
#[1] "abcde.fg"
NOTE: This solution is direct and doesn't need to paste anything together.

Answer 2

Also, substring with paste will work:
paste(substring(text, c(1,6), c(5,7)), collapse=".")
"abcde.fg"
The substring function accepts vector start-stop arguments and "splits" the string at the desired locations. We then can paste these elements together and with the collapse argument.
Without relying on the vector arguments, we could use the newer and recommended substr function:
paste(c(substr(text, 1, 5), substr(text, 6,7)), collapse=".")
[1] "abcde.fg"
Note that as mentioned by konrad-rudolph, this will create a copy of the vector.