CODEWITHSUNDEEP
rvector
wangshuai
wangshuai

Reputation: 11

compatea value in two vectors and assign the compared results into a new vector in R

I have a vector to be append, and here is the code,which is pretty slow due to the nrow is big.

All I want to is to speed up. I have tried c() and append() and both seems not fast enough. And I checkd Efficiently adding or removing elements to a vector or list in R?

Here is the code:

compare<-vector()

for (i in 1:nrow(domin)){

  for (j in 1:nrow(domin)){
      a=0
    if ((domin[i,]$GPA>domin[j,]$GPA) & (domin[i,]$SAT>domin[j,]$SAT)){
      a=1  
    }
    compare<-c(compare,a)
  }
  print(i)
}

I found it is hard to figure out the index for the compare if I use

   #compare<-rep(0,times=nrow(opt_predict)*nrow(opt_predict))

Upvotes: 1

Views: 140

Answers (1)

Frank
Frank

Reputation: 66819

The information you want would be better placed in a matrix:

v1 <- 1:3
v2 <- c(1,2,2)
mat1 <- outer(v1,v1,`>`)
mat2 <- outer(v2,v2,`>`)
both <- mat1 & mat2

To see which positions the inequality holds for, use which:

which(both,arr.ind=TRUE)
#      row col
# [1,]   2   1
# [2,]   3   1

Comments:

  • This answer should be a lot faster than your loop. However, you are really just sorting two vectors, so there is probably a faster way to do this than taking the exhaustive set of inequalities...

  • In your case, there is only a partial ordering (since, for a given i and j, it is possible that neither one is strictly greater than the other in both dimensions). If you were satisfied with sorting first on v1 and then on v2, you could use the data.table package to easily get a full ordering:

    set.seed(1)
v1 <- sample.int(10,replace=TRUE)
v2 <- sample.int(10,replace=TRUE)

require(data.table)
DT <- data.table(v1,v2)
setkey(DT)
DT[,rank:=.GRP,by='v1,v2']

    which gives

        v1 v2 rank
 1:  1  8    1
 2:  3  3    2
 3:  3  8    3
 4:  4  2    4
 5:  6  7    5
 6:  7  4    6
 7:  7 10    7
 8:  9  5    8
 9: 10  4    9
10: 10  8   10

    It depends on what you were planning to do next.

Upvotes: 6

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