Matching numbers by their order when in two different vectors - r

Question

The title does not really do this question justice, but I could not think of any other way to phrase the question. I can best explain the problem with an example.
Let's say we have two vectors of numbers (each of which are always going to be ascending and unique):
vector1 <- c(1,3,10,11,24,26,30,31)
vector2 <- c(5,9,15,19,21,23,28,35)
What I am trying to do is create a function that will take these two vectors and match them in the following way:
1) Start with the first element of vector1 (in this case, 1)
2) Go to vector2 and match the element from #1 with the first element in vector 2 that is bigger than it (in this case, 5)
3) Go back to vector1 and skip all elements less than the value in #2 we found (in this case, we skip 3, and grab 10)
4) Go back to vector2 and skip all elements less than the value in #3 we found (in this case, we skip 9 and grab 15)
5) repeat until we are done with all elements.
The resulting two vectors we should have are:
result1 = c(1,10,24,30)
result2 = c(5,15,28,35)
My current solution goes something like this, but I believe it might be highly inefficient:
# establishes where we start from the vector2 numbers
# just in case we have vector1 <- c(5,8,10)
# and vector2 <- c(1,2,3,4,6,7). We would want to skip the 1,2,3,4 values
i <- 1
while(vector2[i]<vector1[1]){
i <- i+1
}
# starts the result1 vector with the first value from the vector1
result1 <- vector1[1]
# starts the result2 vector empty and will add as we loop through
result2 <- c()
# super complicated and probably hugely inefficient loop within a loop within a loop
# i really want to avoid doing this, but I cannot think of any other way to accomplish this
for(j in 1:length(vector1)){
while(vector1[j] > vector2[i] && (i+1) <= length(vector2)){
result1 <- c(result1,vector1[j])
result2 <- c(result2,vector2[i])
while(vector1[j] > vector2[i+1] && (i+2) <= length(vector2)){
i <- i+1
}
i <- i+1
}
}
## have to add on the last vector2 value cause while loop skips it
## if it doesn't exist (there are no more vector2 values bigger) we put in an NA
if(result1[length(result1)] < vector2[i]){
result2 <- c(result2,vector2[i])
}
else{
### we ran out of vector2 values that are bigger
result2 <- c(result2,NA)
}

Answer 1

This is really difficult to explain. Just call it magic :)
vector1 <- c(1,3,10,11,24,26,30,31)
vector2 <- c(5,9,15,19,21,23,28,35)
## another case
# vector2 <- c(0,9,15,19,21,23,28,35)
## handling the case where vector2 min value(s) are < vector1 min value
if (any(idx <- which(min(vector1) >= vector2)))
vector2 <- vector2[-idx]
## interleave the two vectors
tmp <- c(vector1,vector2)[order(c(order(vector1), order(vector2)))]
## if we sort the vectors, which pairwise elements are from the same vector
r <- rle(sort(tmp) %in% vector1)$lengths
## I want to "remove" all the pairwise elements which are from the same vector
## so I again interleave two vectors:
## the first will be all TRUEs because I want the first instance of each *new* vector
## the second will be all FALSEs identifying the elements I want to throw out because
## there is a sequence of elements from the same vector
l <- rep(1, length(r))
ord <- c(l, r - 1)[order(c(order(r), order(l)))]
## create some dummy TRUE/FALSE to identify the ones I want
res <- sort(tmp)[unlist(Map(rep, c(TRUE, FALSE), ord))]
setNames(split(res, res %in% vector2), c('result1', 'result2'))
# $result1
# [1] 1 10 24 30
#
# $result2
# [1] 5 15 28 35
obviously this will only work if both vectors are ascending and unique which you said
EDIT:
works with duplicates:
vector1 <- c(1,3,10,11,24,26,30,31)
vector2 <- c(5,9,15,19,21,23,28,35)
vector2 <- c(0,9,15,19,21,23,28,35)
vector2 <- c(1,3,3,5,7,9,28,35)
f <- function(v1, v2) {
if (any(idx <- which(min(vector1) >= vector2)))
vector2 <- vector2[-idx]
vector1 <- paste0(vector1, '.0')
vector2 <- paste0(vector2, '.00')
n <- function(x) as.numeric(x)
tmp <- c(vector1, vector2)[order(n(c(vector1, vector2)))]
m <- tmp[1]
idx <- c(TRUE, sapply(1:(length(tmp) - 1), function(x) {
if (n(tmp[x + 1]) > n(m)) {
if (gsub('^.*\\.','', tmp[x + 1]) == gsub('^.*\\.','', m))
FALSE
else {
m <<- tmp[x + 1]
TRUE
}
} else FALSE
}))
setNames(split(n(tmp[idx]), grepl('\\.00$', tmp[idx])), c('result1','result2'))
}
f(vector1, vector2)
# $result1
# [1] 1 10 30
#
# $result2
# [1] 3 28 35