9 mtapply()
Being a multivariate version of tapply()
, mtapply
applies a function over an array by a list of indices.
The two required inputs are the object X
and list of indices INDEX
. The optional inputs are the function to apply FUN
and ...
, which passses to mapply
. For the first three inputs, see the documentation for tapply()
9 for more information; for the fourth, see mapply()
10. The output is typically a list of vectors or matrices, depending on the inputs and funciton being passed.
9.0.1 Multivariate tapply()
A <- mtcars[, c('mpg', 'wt', 'disp')] # Targets.
B <- mtcars[, c('gear', 'am', 'carb')] # Indices.
mtapply(A, B, mean) # Output
## $mpg_by_gear
## 3 4 5
## 16.10667 24.53333 21.38000
##
## $wt_by_am
## 0 1
## 3.768895 2.411000
##
## $disp_by_carb
## 1 2 3 4 6 8
## 134.2714 208.1600 275.8000 308.8200 145.0000 301.0000