Conditionally Remove Character of a Vector Element in R - regex

Question

I have (sometimes incomplete) data on addresses that looks like this:
data <- c("1600 Pennsylvania Avenue, Washington DC",
",Siem Reap,FC,", "11 Wall Street, New York, NY", ",Addis Ababa,FC,")
I need to remove the first and/or last character if either one of them are a comma.
So far, I have:
for(i in 1:length(data)){
lastchar <- nchar(data[i])
sec2last <- nchar(data[i]) - 1
if(regexpr(",",data[i])[1] == 1){
data[i] <- substr(data[i],2, lastchar)
}
if(regexpr(",",data[i])[1] == nchar(data[i])){
data[i] <- substr(data[i],1, sec2last)
}
}
data
which works for the first character, but not the last character. How can I modify the second if statement or otherwise accomplish my goal?

Answer 1

You could try the below code which remove the comma present at the start or at the end,
> data <- c("1600 Pennsylvania Avenue, Washington DC",
+ ",Siem Reap,FC,", "11 Wall Street, New York, NY", ",Addis Ababa,FC,")
> gsub("(?<=^),|,(?=$)", "", data, perl=TRUE)
[1] "1600 Pennsylvania Avenue, Washington DC"
[2] "Siem Reap,FC"
[3] "11 Wall Street, New York, NY"
[4] "Addis Ababa,FC"
Pattern explanation:
(?<=^), In regex (?<=) called positive look-behind. In our case it asserts What precedes the comma must be a line start ^. So it matches the starting comma.
| Logical OR operator usually used to combine(ie, ORing) two regexes.
,(?=$) Lookahead aseerts that what follows comma must be a line end $. So it matches the comma present at the line end.