Transforms a matrix of items into a new matrix where the select polytomous items have been converted into comparable dichotomous items with the same information.
poly2dich(data, which.items = 1:ncol(data), sep = "_cat.")an object of class data.frame or matrix
a vector indicating which items should be transformed into the dichotomous form. Default uses all input items
character vector pattern to append to each item name in data
Returns an integer matrix
Chalmers, R., P. (2012). mirt: A Multidimensional Item Response Theory Package for the R Environment. Journal of Statistical Software, 48(6), 1-29. doi:10.18637/jss.v048.i06
# \donttest{
data(Science)
head(Science)
#> Comfort Work Future Benefit
#> 1 4 4 3 2
#> 2 3 3 3 3
#> 3 3 2 2 3
#> 4 3 2 2 3
#> 5 3 4 4 1
#> 6 4 4 3 3
newScience <- poly2dich(Science)
head(newScience)
#> Comfort_cat.1 Comfort_cat.2 Comfort_cat.3 Comfort_cat.4 Work_cat.1
#> [1,] 0 0 0 1 0
#> [2,] 0 0 1 0 0
#> [3,] 0 0 1 0 0
#> [4,] 0 0 1 0 0
#> [5,] 0 0 1 0 0
#> [6,] 0 0 0 1 0
#> Work_cat.2 Work_cat.3 Work_cat.4 Future_cat.1 Future_cat.2 Future_cat.3
#> [1,] 0 0 1 0 0 1
#> [2,] 0 1 0 0 0 1
#> [3,] 1 0 0 0 1 0
#> [4,] 1 0 0 0 1 0
#> [5,] 0 0 1 0 0 0
#> [6,] 0 0 1 0 0 1
#> Future_cat.4 Benefit_cat.1 Benefit_cat.2 Benefit_cat.3 Benefit_cat.4
#> [1,] 0 0 1 0 0
#> [2,] 0 0 0 1 0
#> [3,] 0 0 0 1 0
#> [4,] 0 0 0 1 0
#> [5,] 1 1 0 0 0
#> [6,] 0 0 0 1 0
newScience2 <- poly2dich(Science, which.items = 2)
head(newScience2)
#> Comfort Work_cat.1 Work_cat.2 Work_cat.3 Work_cat.4 Future Benefit
#> 1 4 0 0 0 1 3 2
#> 2 3 0 0 1 0 3 3
#> 3 3 0 1 0 0 2 3
#> 4 3 0 1 0 0 2 3
#> 5 3 0 0 0 1 4 1
#> 6 4 0 0 0 1 3 3
# }