[R] code for "permutative" operation

[Sascha Vieweg]

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.

-- 
Sascha Vieweg, saschaview at gmail.com