Function to compute the number of subjects.

nsub(id, data)

Arguments

id

vector to specify a subject id variable.

data

optional data frame that contains the variable specified above.

Details

The function simply computes the number of subjects in a long-format dataset (i.e., the number of unique values of the id variable).

Value

A scalar.

Author

Wolfgang Viechtbauer wvb@wvbauer.com

Examples

# illustrative dataset dat <- data.frame(subj=rep(1:4, each=5), obs = 1:5, age = rep(c(20,31,27,22), each=5), stress = c(2,3,NA,4,2, 3,3,NA,3,NA, 1,1,2,6,4, 1,2,1,3,1)) dat
#> subj obs age stress #> 1 1 1 20 2 #> 2 1 2 20 3 #> 3 1 3 20 NA #> 4 1 4 20 4 #> 5 1 5 20 2 #> 6 2 1 31 3 #> 7 2 2 31 3 #> 8 2 3 31 NA #> 9 2 4 31 3 #> 10 2 5 31 NA #> 11 3 1 27 1 #> 12 3 2 27 1 #> 13 3 3 27 2 #> 14 3 4 27 6 #> 15 3 5 27 4 #> 16 4 1 22 1 #> 17 4 2 22 2 #> 18 4 3 22 1 #> 19 4 4 22 3 #> 20 4 5 22 1
# compute the number of subjects nsub(subj, dat)
#> [1] 4
# or specify the subject variable this way nsub(dat$subj)
#> [1] 4