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
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