Dear all,
 
I found a difference between the indexing of an array and that of a matrix when there are NA's in the index array. The screen copy is as follows. 
 
> A <- array(NA, dim=6)
> A
[1] NA NA NA NA NA NA
> idx <- c(1,NA,NA,4,5,6)
> B <- c(10,20,30,40,50,60)
> A[idx] <- B
> A
[1] 10 NA NA 40 50 60
> AA <- matrix(NA,6,1)
> AA
     [,1]
[1,]   NA
[2,]   NA
[3,]   NA
[4,]   NA
[5,]   NA
[6,]   NA
> AA[idx,1] <- B
> AA
     [,1]
[1,]   10
[2,]   NA
[3,]   NA
[4,]   20
[5,]   30
[6,]   40
> 
 
In the case of a array, we miss the elements (20 and 30) in B corresponding to the NA's in the index array. In the case of a matrix, 20 and 30 are assigned to the elements indexed by the indexes following the NA's. Is this a reasonable behavior. Thanks in advance for explanation.
 
-MY

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