[R] Using apply with more than one matrix

[Waichler, Scott R]

Here is a working example with no random parts.  Thanks for your patience and if I'm still off the mark with my presentation I'll drop the matter.  

v <- c(NA, 1.5, NA, NA,
       NA, 1.1, 0.5, NA,
       NA, 1.3, 0.4, 0.9)
a1 <- array(v, dim=c(2,2,3))
m1 <- matrix(c(NA, 1.5, 2.1, NA), ncol=2, byrow=T)
m2 <- matrix(c(1.56, 1.64, 1.16, 2.92), ncol=2)
condition1 <- !is.na(m1)& m1 > m2

ans <- matrix(NA, ncol=2, nrow=2) # initialize
for(i in 1:2) {
  for(j in 1:2) {
    ind.not.na <- which(!is.na(a1[i,j,]))
    if(condition1[i,j] && length(ind.not.na) > 0) ans[i,j] <- a1[i,j,ind.not.na[1]] + m2[i,j]
  }
}
ans
     [,1] [,2]
[1,]   NA 1.66
[2,] 3.14   NA

Let me try asking again in words.  If I have multiple matrices or slices of 3d arrays that are the same dimension, is there a way to pass them all to apply, and have apply take care of looping through i,j?  I understand that apply has just one input object x.  I want to work on more than one array object at once using a custom function that has this characteristic:  in order to compute the answer at i,j I need a result from higher order array at the same i,j.  This is what I tried to demonstrate in my example above.

Thanks,
Scott