On Oct 28, 2009, at 5:22 PM, Carl Witthoft wrote:
Just wondering if it's possible to have an item with no content at
all. Here's what I was hoping to do, inside a larger function that
acts on a 3-D array.
I want to enter, as one of the arguments to the main function, the
index over which I'm going to do some action. For example, if the
action were to calc a sum, I'd specify a given axis and report the
sums along that axis for all coordinate pairs on the other two axes
of the array.
So, I'd hoped to define three variables sort of like
A1 = 'i'
A2 = 'j'
A3 = {nothing}
Forget the variables,,,,
then a loop over i and j around a command something like (not the
real code, but you get the idea):
... and forget the loops.
> sum(thearray[get(A1),get(A2),get(A3)])
which in my optimistic mind would turn into "sum(thearray[i,j,])"
> smlarr <- array(1:27, c(3,3,3))
> smlarr
, , 1
[,1] [,2] [,3]
[1,] 1 4 7
[2,] 2 5 8
[3,] 3 6 9
, , 2
[,1] [,2] [,3]
[1,] 10 13 16
[2,] 11 14 17
[3,] 12 15 18
, , 3
[,1] [,2] [,3]
[1,] 19 22 25
[2,] 20 23 26
[3,] 21 24 27
> sum( smlarr[1:2, 2, ] )
# could use any named or unnamed vectors whose range is within that
defined for the array
#[1] 81
. The problem is that I don't see any way to have nothing
whatsoever in the selected index. A value of A3='' gets interpreted
as a 'blank' name or some such.
I solved the problem by setting the value to
A3 = 'seq(1,dim(thearray)[3])' (or similar),
but just would like to know in general if there is some way to put
nothing at all in there. (NA and NULL don't work)
--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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