R：使用Mapply来避免循环

Question

I have following code which I perform with for loop to generate a 3D array "newarr".

n1<-c(1,2,3,4,5)
n2<-c(3,4,5,6,7)
n3<- c(4,5,6,7,8)

afun <- function(y,p,q,r){
              calc=1/(1+(((y-p)/q)^(2*r)))
              return(calc)
        }

newarr<- array(dim = c(4,5,5))
Amat<-matrix(data=c(1:10,NA,NA,NA,NA,15:20),nrow = 4,ncol = 5)
Bmat<-matrix(data=c(1:6,NA,NA,NA,NA,11:20),nrow = 4,ncol = 5)
Qmat<- +(!is.na(Amat) & !is.na(Bmat))

for(i in 1:5){
     res<-afun(Amat,n1[i],n2[i],n3[i])
     newarr[,,i]<- res 
}

I want to use Mapply (or any apply function) instead of for loop. arr2 <- array((mapply(function(x,y,n1,n2,n3) if(x==1) afun(y,n1,n2,n3) else 0,Qmat,Amat,n1,n2,n3)),c(4,5,5))

The following code seems to help but without condition as described further:
newarr <- array(mapply(afun, n1,n2,n3, MoreArgs = list(y=Amat)), c(4,5,5))

I want to include a condition by using Qmat (a 4x5 matrix with 0 and 1), so that when '0' is observed, no operation should be performed and return '0'value to fill matrix. For 1s in Qmat, perform 'afun' function and return the value to "newarr" to form a 3D matrix.

Thanks for the help!!

Answer 1

This will give you the desired result:

newarr <- array(mapply(afun, n1,n2,n3, MoreArgs = list(y=Amat)), c(4,5,5))

this is using the implicit SIMPLIFY=TRUE of mapply(). With SIMPLIFY=TRUE each result is reduced to a vector. (a matrix is a vector with a dimension attribute)
Another variant is

array(unlist(mapply(afun, n1,n2,n3, MoreArgs = list(y=Amat), SIMPLIFY = FALSE)), c(4,5,5))

here you will get a list of matrices as result from mapply(). You have to unlist.