Number of Subjects

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