This function constructs all possible k-way combinations of an input vector.
It is primarily useful when used in conjunction with the mdirt function,
though users may have other uses for it as well. See expand.grid for more
flexible combination formats.
Arguments
- theta
the vector from which all possible combinations should be obtained
- nfact
the number of observations (and therefore the number of columns to return in the matrix of combinations)
- intercept
logical; should a vector of 1's be appended to the first column of the result to include an intercept design component? Default is
FALSE
References
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
Author
Phil Chalmers rphilip.chalmers@gmail.com
Examples
# all possible joint combinations for the vector -4 to 4
thetaComb(-4:4, 2)
#> [,1] [,2]
#> [1,] -4 -4
#> [2,] -3 -4
#> [3,] -2 -4
#> [4,] -1 -4
#> [5,] 0 -4
#> [6,] 1 -4
#> [7,] 2 -4
#> [8,] 3 -4
#> [9,] 4 -4
#> [10,] -4 -3
#> [11,] -3 -3
#> [12,] -2 -3
#> [13,] -1 -3
#> [14,] 0 -3
#> [15,] 1 -3
#> [16,] 2 -3
#> [17,] 3 -3
#> [18,] 4 -3
#> [19,] -4 -2
#> [20,] -3 -2
#> [21,] -2 -2
#> [22,] -1 -2
#> [23,] 0 -2
#> [24,] 1 -2
#> [25,] 2 -2
#> [26,] 3 -2
#> [27,] 4 -2
#> [28,] -4 -1
#> [29,] -3 -1
#> [30,] -2 -1
#> [31,] -1 -1
#> [32,] 0 -1
#> [33,] 1 -1
#> [34,] 2 -1
#> [35,] 3 -1
#> [36,] 4 -1
#> [37,] -4 0
#> [38,] -3 0
#> [39,] -2 0
#> [40,] -1 0
#> [41,] 0 0
#> [42,] 1 0
#> [43,] 2 0
#> [44,] 3 0
#> [45,] 4 0
#> [46,] -4 1
#> [47,] -3 1
#> [48,] -2 1
#> [49,] -1 1
#> [50,] 0 1
#> [51,] 1 1
#> [52,] 2 1
#> [53,] 3 1
#> [54,] 4 1
#> [55,] -4 2
#> [56,] -3 2
#> [57,] -2 2
#> [58,] -1 2
#> [59,] 0 2
#> [60,] 1 2
#> [61,] 2 2
#> [62,] 3 2
#> [63,] 4 2
#> [64,] -4 3
#> [65,] -3 3
#> [66,] -2 3
#> [67,] -1 3
#> [68,] 0 3
#> [69,] 1 3
#> [70,] 2 3
#> [71,] 3 3
#> [72,] 4 3
#> [73,] -4 4
#> [74,] -3 4
#> [75,] -2 4
#> [76,] -1 4
#> [77,] 0 4
#> [78,] 1 4
#> [79,] 2 4
#> [80,] 3 4
#> [81,] 4 4
# all possible binary combinations for four observations
thetaComb(c(0,1), 4)
#> [,1] [,2] [,3] [,4]
#> [1,] 0 0 0 0
#> [2,] 1 0 0 0
#> [3,] 0 1 0 0
#> [4,] 1 1 0 0
#> [5,] 0 0 1 0
#> [6,] 1 0 1 0
#> [7,] 0 1 1 0
#> [8,] 1 1 1 0
#> [9,] 0 0 0 1
#> [10,] 1 0 0 1
#> [11,] 0 1 0 1
#> [12,] 1 1 0 1
#> [13,] 0 0 1 1
#> [14,] 1 0 1 1
#> [15,] 0 1 1 1
#> [16,] 1 1 1 1
# all possible binary combinations for four observations (with intercept)
thetaComb(c(0,1), 4, intercept=TRUE)
#> [,1] [,2] [,3] [,4] [,5]
#> [1,] 1 0 0 0 0
#> [2,] 1 1 0 0 0
#> [3,] 1 0 1 0 0
#> [4,] 1 1 1 0 0
#> [5,] 1 0 0 1 0
#> [6,] 1 1 0 1 0
#> [7,] 1 0 1 1 0
#> [8,] 1 1 1 1 0
#> [9,] 1 0 0 0 1
#> [10,] 1 1 0 0 1
#> [11,] 1 0 1 0 1
#> [12,] 1 1 1 0 1
#> [13,] 1 0 0 1 1
#> [14,] 1 1 0 1 1
#> [15,] 1 0 1 1 1
#> [16,] 1 1 1 1 1