"Alberto Monteiro" <[EMAIL PROTECTED]> writes:
> Why is this an error?
>
> mat <- matrix(1:64, 8, 8)
> x <- y <- 1:8
> z <- outer(x, y, function(x, y) mat[x,y])
>
> when this is not an error:
>
> mat <- matrix(1:64, 8, 8)
> x <- y <- 1:8
> z <- outer(x, y, function(x, y) paste("mat[", x, ",", y, "]", sep=""))
Because, outer vectorizes, and e.g.,
mat[1:2,1:2] has *four* elements,
whereas paste("mat[", 1:2, ",", 1:2, "]", sep="") has only two.
So mat[x,y] will be 64x64 ad dimensions don't fit.
It works if you use the matrix index:
> z <- outer(x, y, function(x, y) mat[cbind(x,y)])
> z
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8]
[1,] 1 9 17 25 33 41 49 57
[2,] 2 10 18 26 34 42 50 58
[3,] 3 11 19 27 35 43 51 59
[4,] 4 12 20 28 36 44 52 60
[5,] 5 13 21 29 37 45 53 61
[6,] 6 14 22 30 38 46 54 62
[7,] 7 15 23 31 39 47 55 63
[8,] 8 16 24 32 40 48 56 64
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