[R] programming question

[Adrian Dusa]

Dear list,

I have a vector of numbers, let's say:

myvec <- c(2, 8, 24, 26, 51, 57, 58, 78, 219)

My task is to reduce this vector to non-reducible numbers; small numbers can 
cross-out some of the larger ones, based on a function let's say called 
reduce()

If I apply the function to the first element 2, my vector gets shorted to:
> (myvec <- reduce(myvec[1]))
 [1]   2   24   51   57   58   78  219

The next element that can further reduce the vector is the second (24) and a 
next iteration further reduces it and so on, until nothing can be reduced.

The question is, what is the best programming technique to achieve this?

My crude solution is:
####
position <- 1 # start with the first position in the vector (smallest number)
while(position < length(myvec)) {
    myvec <- reduce(myvec[position])
    position <- position + 1
    }
####

Is there a better programming approach?
Some vectors have lengths of millions, so this one takes a very long time.

Thanks in advance,
Adrian



PS: below is a self-contained example:
The initial vector corresponds to the following lines in a base 3 matrix:
      [,1] [,2] [,3] [,4] [,5]
   2     0    0    0    0    2
   8     0    0    0    2    2
  24     0    0    2    2    0
  26     0    0    2    2    2
  51     0    1    2    2    0
  57     0    2    0    1    0
  58     0    2    0    1    1
  78     0    2    2    2    0
 219     2    2    0    1    0

In the first iteration, the first element 2 eliminates 8 and 26 because both 
contain number 2 in the last position (first line being shorter).
The element 24 eliminates 51 and 78, and so on.

`findSubsets2` <-
function(element) {
    require(QCA)
    base3row <- getRow(rep(3,5), element, zerobased=TRUE)
    increment <- function(x, y) {
        a <- x
        for (i in 1:2) {
            a <- as.vector(outer(y, a, "+"))
            x <- c(x, a)
            }
        return(x)
        }
    indices <- which(base3row == 0)
    mbase <- c(81, 27, 9, 3, 1)
    for (i in indices) {
        element <- increment(element, mbase[i])
        }
    return(element[-1])
    }

position <- 1
while(position < length(myvec)) {
    falsevector <- findSubsets2(myvec[position])
    myvec <- setdiff(myvec, falsevector)
    position <- position + 1
    }




-- 
Adrian Dusa
Romanian Social Data Archive
1, Schitu Magureanu Bd
050025 Bucharest sector 5
Romania
Tel./Fax: +40 21 3126618 \
          +40 21 3120210 / int.101