Description Usage Arguments Value Note Author(s) See Also Examples
Given a function f()
that takes a vector of indices, and an
array of arbitrary dimensions, apply f()
to the elements of a
1 
a 
Array 
f 
Function that takes a vector argument of the same length as

... 
Further arguments supplied to 
Returns a matrix of the same dimensions as a
Tamas Papp suggests the oneliner
function(a, f, ...){array(apply(as.matrix(expand.grid(lapply(dim(a),seq_len),KEEP.OUT.ATTRS=FALSE)),1,f,...),dim(a))}
which is functionally identical to do.index()
; but
it is no faster than the version implemented in the package, and (IMO)
is harder to read.
Further note that function arow()
is much much faster than
do.index()
; it is often possible to rephrase a call to
do.index()
as a call to arow()
; do this where possible
unless the additional code opacity outweighs the speed savings.
Robin K. S. Hankin, with improvements by Gabor Grothendieck and Martin Maechler, via the R help list
1 2 3 4 5 6 7 8 9 10 11 12 13 14  a < array(0,c(2,3,4))
b < array(rpois(60,1),c(3,4,5))
f1 < function(x){sum(x)}
f2 < function(x){sum((x1)^2)}
f3 < function(x){b[t(x)]}
f4 < function(x){sum(x)%%2}
f5 < function(x,u){x[u]}
do.index(a,f1) # should match arow(a,1)+arow(a,2)+arow(a,3)
do.index(a,f2)
do.index(a,f3) # same as apltake(b,dim(a))
do.index(a,f4) # Male/female toilets at NOC
do.index(a,f5,2) # same as arow(a,2)

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