问题
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 would like to do the following actions using pipes:
rownames(mtcars) <- as.character(1:nrow(mtcars))
so that it looks like:
library(magrittr)
mtcars <-
mtcars %>%
...???
Note that @akrun's answer shows that if the pipe is used in conjection with a function that coerces the data frame into a tbl_df, the row names will be lost.
回答1:
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
回答2:
Other possibility is to use set_rownames alias from magrittr library.
mtcars <-
mtcars %>%
set_rownames(as.character(1:nrow(mtcars)))
回答3:
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.
回答4:
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)
来源：https://stackoverflow.com/questions/38136662/how-to-add-a-row-names-to-a-data-frame-in-a-magrittr-chain