apply function that always returns a numeric matrix

The function is modeled after `vapply`, but always returns a matrix with one row for each iteration. You need to provide the number of elements each function call produces beforehand (i.e. the number of resulting columns). For a more flexible version where you don't need to provide the number of columns see msply_dbl

mply_dbl(x, FUN, ncol = 1, ...)

msply_dbl(x, FUN, ...)

Arguments

x	a vector that will be passed to `vapply` or a matrix that will be passed to apply with MARGIN=1.
FUN	the function that returns a vector of length ncol
ncol	the length of the vector returned by `FUN`.
...	additional arguments to FUN

Value

a matrix of size length(x) x ncol

Functions

• mply_dbl: apply function that always returns a numeric matrix

• msply_dbl: flexible version that automatically infers the number of columns

Examples

  # Behaves similar to sapply(), but it always returns a matrix
  t(sapply(1:5, function(i) c(i - i/3, i, i + i/3)))
#>           [,1] [,2]     [,3]
#> [1,] 0.6666667    1 1.333333
#> [2,] 1.3333333    2 2.666667
#> [3,] 2.0000000    3 4.000000
#> [4,] 2.6666667    4 5.333333
#> [5,] 3.3333333    5 6.666667
  proDA:::mply_dbl(1:5, function(i) c(i - i/3, i, i + i/3), ncol=3)
#>           [,1] [,2]     [,3]
#> [1,] 0.6666667    1 1.333333
#> [2,] 1.3333333    2 2.666667
#> [3,] 2.0000000    3 4.000000
#> [4,] 2.6666667    4 5.333333
#> [5,] 3.3333333    5 6.666667

  # Which can avoid some bad surprises
  t(sapply(1:5, identity))
#>      [,1] [,2] [,3] [,4] [,5]
#> [1,]    1    2    3    4    5
  proDA:::mply_dbl(1:5, identity)
#>      [,1]
#> [1,]    1
#> [2,]    2
#> [3,]    3
#> [4,]    4
#> [5,]    5


  # Works also with matrix input
  mat <- matrix(1:20, ncol=4)
  mat
#>      [,1] [,2] [,3] [,4]
#> [1,]    1    6   11   16
#> [2,]    2    7   12   17
#> [3,]    3    8   13   18
#> [4,]    4    9   14   19
#> [5,]    5   10   15   20
  proDA:::msply_dbl(mat, function(i) rep(i, each=2))
#>      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8]
#> [1,]    1    1    6    6   11   11   16   16
#> [2,]    2    2    7    7   12   12   17   17
#> [3,]    3    3    8    8   13   13   18   18
#> [4,]    4    4    9    9   14   14   19   19
#> [5,]    5    5   10   10   15   15   20   20