Using dplyr, how should I create a column of strings repeating a character based on the value of another column?

Question

With mtcars for example, I'd like to create a new column carb_dots such that when carb = 4, carb_dots = "...."

Using dplyr, I've tried

library(dplyr)
mtcars2 <- mtcars %>% mutate(carb_dots = rep(".", carb))

This errors with

Error in mutate_impl(.data, dots) : Evaluation error: invalid 'times' argument.

What should I do? Thanks for your suggestions.

Answer 1

With the addition of stringr, you can do:

mtcars %>% 
 mutate(carb_dots = str_dup(".", carb))

    mpg cyl  disp  hp drat    wt  qsec vs am gear carb carb_dots
1  21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4      ....
2  21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4      ....
3  22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1         .
4  21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1         .
5  18.7   8 360.0 175 3.15 3.440 17.02  0  0    3    2        ..
6  18.1   6 225.0 105 2.76 3.460 20.22  1  0    3    1         .
7  14.3   8 360.0 245 3.21 3.570 15.84  0  0    3    4      ....
8  24.4   4 146.7  62 3.69 3.190 20.00  1  0    4    2        ..
9  22.8   4 140.8  95 3.92 3.150 22.90  1  0    4    2        ..
10 19.2   6 167.6 123 3.92 3.440 18.30  1  0    4    4      ....

Answer 2

We can use strrep

library(dplyr)
mtcars %>% 
      mutate(carb_dots = strrep(".", carb))
#                     mpg cyl  disp  hp drat    wt  qsec vs am gear carb carb_dots
#Mazda RX4           21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4      ....
#Mazda RX4 Wag       21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4      ....
#Datsun 710          22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1         .
#Hornet 4 Drive      21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1         .
#Hornet Sportabout   18.7   8 360.0 175 3.15 3.440 17.02  0  0    3    2        ..
#Valiant             18.1   6 225.0 105 2.76 3.460 20.22  1  0    3    1         .
#Duster 360          14.3   8 360.0 245 3.21 3.570 15.84  0  0    3    4      ....
#...

---

If we need to use rep

mtcars %>%
   rowwise %>%
   mutate(carb_dots = paste(rep(".", carb), collapse=""))