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

d <- read.table(text='Column1   Column2  
 1         A 
 1         B 
 2         C 
 2         D 
 3         E 
 4         F', header=TRUE)

transform(d, 
    Column1.new = ifelse(duplicated(Column1) | duplicated(Column1, fromLast=TRUE), 
                         paste(Column1, ave(Column1, Column1, FUN=seq_along), sep='_'), 
                         Column1))

#   Column1 Column2 Column1.new
# 1       1       A         1_1
# 2       1       B         1_2
# 3       2       C         2_1
# 4       2       D         2_2
# 5       3       E           3
# 6       4       F           4