R Shuffle and randomize columns of a data table

Question

Given a data.table such as:

data.table::data.table(a = c(1,2,3), b = c("red","blue","yellow"), c = c(TRUE, FALSE, TRUE), d = c(21, 45, 34, 26))

   a      b     c  d
1: 1    red  TRUE 21
2: 2   blue FALSE 45
3: 3 yellow  TRUE 34
4: 4  green FALSE 26

where a is a unique row identifier, how could I randomize/anonymize the data so that the columns shuffle within their own column. This would create a random data.table that looks something like:

   a      b     c  d
1: 1  green  TRUE 26
2: 2 yellow FALSE 45
3: 3    red FALSE 21
4: 4   blue  TRUE 34

Answer 1

If it is random for each column that doesn't tie with the rows, then use sample on the columns specified in the .SDcols by looping over them in lapply and assign (:=) the output back to the columns

dt1[, (2:4) := lapply(.SD, sample), .SDcols = 2:4]

-output

dt1
#   a      b     c  d
#1: 1   blue FALSE 34
#2: 2    red  TRUE 21
#3: 3  green FALSE 45
#4: 4 yellow  TRUE 26

---

Or another option is set

for(j in names(dt1)[-1]) {
      set(dt1, i = NULL, j = j, value = sample(dt1[[j]]))
 }

data

dt1 <- data.table::data.table(
      a = c(1,2,3, 4),
      b = c("red","blue","yellow", "green"), 
      c = c(TRUE, FALSE, TRUE, FALSE), 
      d = c(21, 45, 34, 26)
   )