Problem with mutate: seeking to fill each line of a column with samples that differ from one another

I want to create a dataframe in which one column contains a list made of a sample of 4 elements taken from a vector. I need all rows of this variable to contain a different sample.

This is a reproducible example.

library(dplyr)


vec <- LETTERS # The vector we will take a sample from
td <- tibble(id = 1:3)
td |>mutate(smpl = list(sample(vec, 4, replace = FALSE))) |> View()

What I would expect, is to have a different list for each row of the td dataframe, such as:

id    smpl
1     c("Q", "E", "A", "J")
2     c("Z", "A", "F", "T")
3     c("M", "V" "C", "L")

Instead, the same sample repeats line after line:

id    smpl
1     c("Q", "E", "A", "J")
2     c("Q", "E", "A", "J")
3     c("Q", "E", "A", "J")

Any suggestion? I am especially interested in a solution using dplyr, but... there is more than one right way of doing things in R.

Thank you!

Are you looking for something like this ?

I made the assumption of creating a string/character because you were printing character vectors within quotes.

library(dplyr)

vec <- LETTERS # The vector we will take a sample from

td <- tibble(id = 1:3)

td %>% group_by(id) %>% mutate(smpl = base::paste(sample(vec,4),collapse = ""))

The result:

> td %>% group_by(id) %>% mutate(smpl = base::paste(sample(vec,4),collapse = ""))
# A tibble: 3 × 2
# Groups:   id [3]
     id smpl 
  <int> <chr>
1     1 SETU 
2     2 VCXW 
3     3 JXIL 

You need to replicate for each row:

td |>
  mutate(smpl = replicate(n(), sample(vec, 4, replace = FALSE), simplify = FALSE)) |>
  as.data.frame() # merely to show it, otherwise tibbles would hide the contents
#   id       smpl
# 1  1 Q, E, A, J
# 2  2 D, R, Q, O
# 3  3 X, G, D, E

Both answers work very well, thank you. I didn't know the function replicate(), which acts as a wrapper around sapply(). It definitely works. However, group_by(id)is more in keeping with the logic of dplyr, so I marked that solution as the answer to this question.

Here is my final code (keeping sample items grouped in a list within one dataframe column, which is what I wanted):

td |> group_by(id) |> 
    mutate(smpl = list(sample(vec, 4, replace = FALSE))) |> 
    as.data.frame()

Thank you, Au p and r2evans!

All the best.