Function that returns the value of a time-invariant variable for each subject.

get.timeinvar(x, id, data, na.rm=TRUE)

## Arguments

x argument to specify the time-invariant variable. argument to specify a subject id variable. optional data frame that contains the variables specified above. logical indicating whether missing values should be removed (default is TRUE).

## Details

The function returns the value of a time-invariant variable for each subject from a dataset in long format.

## Value

The function returns a vector.

## Author

Wolfgang Viechtbauer wvb@wvbauer.com

check.timeinvar

## 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(2,3,1,4,2, 3,3,3,3,3, 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      1
#> 4     1   4  20      4
#> 5     1   5  20      2
#> 6     2   1  31      3
#> 7     2   2  31      3
#> 8     2   3  31      3
#> 9     2   4  31      3
#> 10    2   5  31      3
#> 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
# get age of each subject
get.timeinvar(age, subj, data=dat)
#>  1  2  3  4
#> 20 31 27 22
# age value is sometimes NA for the 2nd subject (not a problem)
dat$age[6:7] <- NA dat #> subj obs age stress #> 1 1 1 20 2 #> 2 1 2 20 3 #> 3 1 3 20 1 #> 4 1 4 20 4 #> 5 1 5 20 2 #> 6 2 1 NA 3 #> 7 2 2 NA 3 #> 8 2 3 31 3 #> 9 2 4 31 3 #> 10 2 5 31 3 #> 11 3 1 27 1 #> 12 3 2 27 1 #> 13 3 3 27 2 #> 14 3 4 27 6 #> 15 3 5 27 4 #> 16 4 1 22 1 #> 17 4 2 22 2 #> 18 4 3 22 1 #> 19 4 4 22 3 #> 20 4 5 22 1get.timeinvar(age, subj, data=dat) #> 1 2 3 4 #> 20 31 27 22 # age value is completely missing for the 2nd subject dat$age[6:10] <- NA
dat
#>    subj obs age stress
#> 1     1   1  20      2
#> 2     1   2  20      3
#> 3     1   3  20      1
#> 4     1   4  20      4
#> 5     1   5  20      2
#> 6     2   1  NA      3
#> 7     2   2  NA      3
#> 8     2   3  NA      3
#> 9     2   4  NA      3
#> 10    2   5  NA      3
#> 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      1get.timeinvar(age, subj, data=dat)
#>  1  3  4
#> 20 27 22
# also show subjects with missing value for time-invariant variable
get.timeinvar(age, subj, data=dat, na.rm=FALSE)
#>  1  2  3  4
#> 20 NA 27 22