How to add a row names to a data frame in a magrittr chain

Question

I want to do the opposite of: Convert row names into first column

Somewhere down the chain of pipes I would like to add row names to the data frame, for example, I w

Answer 1

Other possibility is to use set_rownames alias from magrittr library.

mtcars <- 
  mtcars %>%
  set_rownames(as.character(1:nrow(mtcars)))

Answer 2

You can use row.names<-:

mtcars <- mtcars %>% `row.names<-`(as.character(1:nrow(mtcars)))

Should work. As a demo:

df <- data.frame(x = 1:5, y = 2:6)
df <- df %>% `row.names<-`(letters[1:5])
df

#   x y
# a 1 2
# b 2 3
# c 3 4
# d 4 5
# e 5 6

Answer 3

To actually "do the opposite of: Convert row names into first column" as stated at the top, i.e. turn a column of data into the row names, you'll want tibble::column_to_rownames(), which fits into pipes nicely. (I know your example specified something else, i.e. turning a sequence of numbers into the row names, for which you should use the other answers)

library(tidyverse)
starwars %>% column_to_rownames("name") %>% head()
#>                height mass  hair_color  skin_color eye_color birth_year
#> Luke Skywalker    172   77       blond        fair      blue       19.0
#> C-3PO             167   75        <NA>        gold    yellow      112.0
#> R2-D2              96   32        <NA> white, blue       red       33.0
#> Darth Vader       202  136        none       white    yellow       41.9
#> Leia Organa       150   49       brown       light     brown       19.0
#> Owen Lars         178  120 brown, grey       light      blue       52.0
#>                gender homeworld species
#> Luke Skywalker   male  Tatooine   Human
#> C-3PO            <NA>  Tatooine   Droid
#> R2-D2            <NA>     Naboo   Droid
#> Darth Vader      male  Tatooine   Human
#> Leia Organa    female  Alderaan   Human
#> Owen Lars        male  Tatooine   Human
#>                                                                                                                                                    films
#> Luke Skywalker                                           Revenge of the Sith, Return of the Jedi, The Empire Strikes Back, A New Hope, The Force Awakens
#> C-3PO                             Attack of the Clones, The Phantom Menace, Revenge of the Sith, Return of the Jedi, The Empire Strikes Back, A New Hope
#> R2-D2          Attack of the Clones, The Phantom Menace, Revenge of the Sith, Return of the Jedi, The Empire Strikes Back, A New Hope, The Force Awakens
#> Darth Vader                                                                 Revenge of the Sith, Return of the Jedi, The Empire Strikes Back, A New Hope
#> Leia Organa                                              Revenge of the Sith, Return of the Jedi, The Empire Strikes Back, A New Hope, The Force Awakens
#> Owen Lars                                                                                          Attack of the Clones, Revenge of the Sith, A New Hope
#>                                          vehicles                starships
#> Luke Skywalker Snowspeeder, Imperial Speeder Bike X-wing, Imperial shuttle
#> C-3PO                                                                     
#> R2-D2                                                                     
#> Darth Vader                                                TIE Advanced x1
#> Leia Organa                 Imperial Speeder Bike                         
#> Owen Lars

^{Created on 2019-03-18 by the reprex package (v0.2.1)}

Answer 4

The tbl_df changes it to row number. So, we don't need to do any extra effort in changing row names.

library(dplyr)
tbl_df(mtcars)

The same applies if we are using data.table

as.data.table(mtcars)

---

As the OP commented about changing the names to something other than the sequence of rows, if we use the same assignment showed in the other post

 mtcars %>%
     `row.names<-`(c(letters, LETTERS)[1:32]) %>%
      group_by(gear) %>%
      slice(1)
#     mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb
#  <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
#1  21.4     6 258.0   110  3.08 3.215 19.44     1     0     3     1
#2  21.0     6 160.0   110  3.90 2.620 16.46     0     1     4     4
#3  26.0     4 120.3    91  4.43 2.140 16.70     0     1     5     2

As we can see, the row names changes to sequence again. So, if we change the row names to something else and do the dplyr chain operations, the previous change is worthless.