Randomly associate elements of two vectors given conditions

Question

I have a data.table of capitals

capitals<-data.table(capital=c(100,50,25,5))
capitals
   capital
1:     100
2:      50
3:      25
4:       5
         


        

Answer 1

For an easily understandable answer: You can first build a column loss in capitals data.frame and then repeatedly sample for those rows which needs to be corrected:

capitals<-data.frame(capital=c(100,50,25,5))
loss=c(45,10,5,1)

capitals$loss <- sample(loss,replace=F)
capitals
   capital loss
1     100    5
2      50   10
3      25    1
4       5   45

for(i in 1:nrow(capitals)) {
    while(capitals[i,2]>capitals[i,1]){
        capitals[i,2] <- sample(loss, 1)
    }
}

capitals
capital loss
1     100    5
2      50   10
3      25    1
4       5    5

(Note that the last row has been corrected)

If replace=F is needed, one can repeat sampling of entire dataframe till all rows satisfy the criteria:

    capitals<-data.frame(capital=c(100,50,25,5))
    loss=c(45,10,5,1)

    capitals$loss <- sample(loss,replace=F)
    capitals
       capital loss
    1     100    5
    2      50   10
    3      25    1
    4       5   45

while (any(capitals$loss > capitals$capital)) { 
                capitals$loss <- sample(loss,replace=F)}

capitals 
  capital loss
1     100   10
2      50   45
3      25    5
4       5    1