How to recode negative values in a set of variables based on if conditional statement in R?

R newbie here. I am currently trying to recode a set of variables in R, such that all negative values within them are recoded as positive values.

Please find simulated data below:

df <- data.frame(ID = c(1001, 1002, 1003, 1004, 1005, 1006, 1007, 1008, 1009, 1010, 1011),
                 measure1 = rnorm(11, mean = 0, sd = 1),
                 measure2 = rnorm(11, mean = 0, sd = 1),
                 measure3 = rnorm(11, mean = 0, sd = 1),
                 measure4 = rnorm(11, mean = 0, sd = 1))

This is the function I've written so far:

df[2:5] <- sapply(df[2:5], function(x) {
  if(x<0) {
  return(x*-1)
}  else {
   return(x)
    }
  })

although I recieve the following errors:

Warning messages:
1: In if (x < 0) { :
  the condition has length > 1 and only the first element will be used
2: In if (x < 0) { :
  the condition has length > 1 and only the first element will be used
3: In if (x < 0) { :
  the condition has length > 1 and only the first element will be used
4: In if (x < 0) { :
  the condition has length > 1 and only the first element will be used

Any ideas on how to make this work?

Thanks!