On Mar 14, 2011, at 4:16 PM, Sascha Vieweg wrote:
On 11-03-14 21:09, David Winsemius wrote:
On Mar 14, 2011, at 3:52 PM, Sascha Vieweg wrote:
Hello, I need some form of a "permutative" operation on a numeric
vector x
x = (v1, v2, v3, ..., vN)
that produces
x.r = (v1, v1+2, v1+v2+v3, ... v1+v2+...+vN)
If the operation is sum() I can run
x <- 5:8
m <- matrix(rep(x, length(x)), ncol=length(x))
(x.r <- rowsum(m * upper.tri(m, diag=TRUE), rep(1, length(x))))
But there's two things I don't know and kindly request help or
comments upon:
(1) What is the fastest code to perfom the forestanding operation?
(2) Is there a more general function for tasks like this, not only
with the sum procedure applied to the vector? Specifically, the
zeros in the matrix may cause problems with other operations than
sum.
Perhaps this:
fplus <- function(x, y) paste(x,y, sep="+")
Reduce(fplus, vv, accumulate=TRUE)
[1] "v1" "v1+v2"
[3] "v1+v2+v3" "v1+v2+v3+v4"
[5] "v1+v2+v3+v4+v5" "v1+v2+v3+v4+v5+v6"
[7] "v1+v2+v3+v4+v5+v6+v7" "v1+v2+v3+v4+v5+v6+v7+v8"
[9] "v1+v2+v3+v4+v5+v6+v7+v8+v9" "v1+v2+v3+v4+v5+v6+v7+v8+v9+v10"
Thanks, David, after trying around I found that one:
x <- 5:8
sapply(1:length(x), function(y) sum(x[1:y]))
I keep your code in my records for operations that cannot be applied
with function names.
I guess I misunderstood your request. Try the somewhat more elegant:
> Reduce("+", x, accum=TRUE)
[1] 5 11 18 26
--
Sascha Vieweg, saschav...@gmail.com
David Winsemius, MD
West Hartford, CT
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