The following command adds a numeric variable that indicates the rownumber to a dataframe:
some_data$.id <- as.numeric(rownames(some_data))
I have a list that contains many dataframes, and I want to add the variable as defined above to every dataframe in that list. I suspect I will need something like lapply for it, but I don't know how exactly. How do I do this?
You could use purrr::map with tibble::rowid_to_column
library(tidyverse)
lst <- list(mtcars, iris)
map(lst, ~rowid_to_column(.x, ".id"))
#[[1]]
# .id mpg cyl disp hp drat wt qsec vs am gear carb
#1 1 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
#2 2 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
#3 3 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
#4 4 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1
#5 5 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2
#...
#
#[[2]]
# .id Sepal.Length Sepal.Width Petal.Length Petal.Width Species
#1 1 5.1 3.5 1.4 0.2 setosa
#2 2 4.9 3.0 1.4 0.2 setosa
#3 3 4.7 3.2 1.3 0.2 setosa
#4 4 4.6 3.1 1.5 0.2 setosa
#5 5 5.0 3.6 1.4 0.2 setosa
#...
For row names (instead of row numbers) simply replace rowid_to_column with rownames_to_column.
mylist <- list(dat1=mtcars, dat2=mtcars)
mynewlist <- lapply(mylist, function(dat){
dat$.id <- rownames(mtcars)
dat
})
> names(mynewlist)
[1] "dat1" "dat2"
> head(mynewlist$dat1)
mpg cyl disp hp drat wt qsec vs am gear carb .id
Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4 Mazda RX4
Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4 Mazda RX4 Wag
Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1 Datsun 710
Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1 Hornet 4 Drive
Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2 Hornet Sportabout
Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1 Valiant
