Adding column if it does not exist

Question

I have a bunch of data frames with different variables. I want to read them into R and add columns to those that are short of a few variables so that they all have a common

Answer 1

Try the following,

library(tidyverse)

mtcars %>%
  tbl_df() %>%
  rownames_to_column("car") %>%
  mutate(top_speed = if ("top_speed" %in% names(.)){return(top_speed)}else{return(NA)},
         mpg = if ("mpg" %in% names(.)){return(mpg)}else{return(NA)}) %>%
  select(car, top_speed, mpg, everything())
# A tibble: 32 x 13
                 car top_speed   mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb
                               
 1         Mazda RX4        NA  21.0     6 160.0   110  3.90 2.620 16.46     0     1     4     4
 2     Mazda RX4 Wag        NA  21.0     6 160.0   110  3.90 2.875 17.02     0     1     4     4
 3        Datsun 710        NA  22.8     4 108.0    93  3.85 2.320 18.61     1     1     4     1
 4    Hornet 4 Drive        NA  21.4     6 258.0   110  3.08 3.215 19.44     1     0     3     1
 5 Hornet Sportabout        NA  18.7     8 360.0   175  3.15 3.440 17.02     0     0     3     2
 6           Valiant        NA  18.1     6 225.0   105  2.76 3.460 20.22     1     0     3     1
 7        Duster 360        NA  14.3     8 360.0   245  3.21 3.570 15.84     0     0     3     4
 8         Merc 240D        NA  24.4     4 146.7    62  3.69 3.190 20.00     1     0     4     2
 9          Merc 230        NA  22.8     4 140.8    95  3.92 3.150 22.90     1     0     4     2
10          Merc 280        NA  19.2     6 167.6   123  3.92 3.440 18.30     1     0     4     4
# ... with 22 more rows

I think the ifelse() doesn't inherit the class from the object.