dplyr: how to use mutate function to make a key combining a prefix string and a sequence of values

Question

Working on a 4 rows data.frame object with dplyr, I want to created a new "id" column combining a prefix string and a sequence of values.

What I expected:

 columnA|columnB|columnC|id
 data    data    data    id-1
 data    data    data    id-2
 data    data    data    id-3
 data    data    data    id-4

What I tried:

 library (dplyr)
 y <- x %>%
        mutate (id =  "id- " & seq(from = 1, to =4, by = 1))

Answer 1

Either:

x %>% mutate(id = paste0('id-', 1:4))

or:

x %>% mutate(id = paste0('id-', row_number()))

or:

x %>% mutate(id = paste0('id-', 1:n()))

gives you what you want:

  columnA columnB columnC   id
1    data    data    data id-1
2    data    data    data id-2
3    data    data    data id-3
4    data    data    data id-4

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Off course this can also be accomplished easily in base R:

x$id <- paste0('id-', 1:nrow(x))

It is better not to use row.names because they are not always numbers (see for example row.names(mtcars)).

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Or using the data.table package:

library(data.table)
setDT(x)[, id := paste0('id-',.I)]