Renaming duplicate strings in R

Question

I have an R dataframe that has two columns of strings. In one of the columns (say, Column1) there are duplicate values. I need to relabel that column so that it would have t

Answer 1

@Cão answer only with base R:

x=read.table(text="
Column1   Column2   #Column1.new
1         A         #1_1
1         B         #1_2
2         C         #2_1
2         D         #2_2
3         E         #3
4         F         #4", stringsAsFactors=F, header=T)

string<-x$Column1
mstring <- make.unique(as.character(string) )
mstring<-sub("(.*)(\\.)([0-9]+)","\\1_\\3",mstring)
y <- rle(string)
tmp <- !duplicated(string) & (string %in% y$values[y$lengths>1])
mstring[tmp]<-gsub("(.*)","\\1_0", mstring[tmp]) 
end <- sub(".*_([0-9]+)","\\1",grep("_([0-9]*)$",mstring,value=T) ) 
beg <- sub("(.*_)[0-9]+","\\1",grep("_([0-9]*)$",mstring,value=T) ) 
newend <- as.numeric(end)+1
mstring[grep("_([0-9]*)$",mstring)]<-paste0(beg,newend)
x$Column1New<-mstring
x