For loop in R list

Question

I am excepting the below code to do the following: - if the current value is smaller then the previous one, change it with the previous one.

But, as you already guessed, it doesn't behave this way. When I print i between iterations, I can see that the transformations are done, but they are not implemented in the drop_rate list.

Any suggestions how to upgrade this code so changes are made in the list?

drop_rate<-list(
x1=c(0.0000000,0.2666667,0.3466667,0.4666667,0.3866667,0.7333333),
x2=c(0.0000000,0.3076923,0.4102564,0.5000000,0.4230769,0.7307692),
x3=c(0.0000000,0.2763158,0.3815789,0.4736842,0.4210526,0.7368421),
x4=c(0.0000000,0.2987013,0.3896104,0.5064935,0.4285714,0.7402597),
x5=c(0.0000000,0.3116883,0.4025974,0.5064935,0.4285714,0.7272727))

for (i in drop_rate){
  if (i[1]>i[2]){i[2]=i[1]}
  if (i[2]>i[3]){i[3]=i[2]}
  if (i[3]>i[4]){i[4]=i[3]}
  print(i)
  if (i[4]>i[5]){i[5]=i[4]}
  print(i)
  if (i[5]>i[6]){i[6]=i[5]}
}

Expected outpot (what should change is delimited with **):

0.0000000,0.2666667,0.3466667,0.4666667,**0.4666667**,0.7333333
0.0000000,0.3076923,0.4102564,0.5000000,**0.5000000**,0.7307692
0.0000000,0.2763158,0.3815789,0.4736842,**0.4736842**,0.7368421
0.0000000,0.2987013,0.3896104,0.5064935,**0.5064935**,0.7402597
0.0000000,0.3116883,0.4025974,0.5064935,**0.5064935**,0.7272727

You need [[ instead of [. also if/else works on a single element i.e. of length 1. I guess you may need to check if all elements are greater than ? — akrun
– akrun, Commented Apr 30, 2020 at 20:30
Put them everywhere, this is what i get: Error in if (i[[1]] > i[[2]]) { : missing value where TRUE/FALSE needed — Stefan
– Stefan, Commented Apr 30, 2020 at 20:33
Nevermind, solved the error. But it's still not doing the transformations. — Stefan
– Stefan, Commented Apr 30, 2020 at 20:35
Can you check my solution below with pmin and Map. If you had showed the expected output, it would be easier to crosscheck — akrun
– akrun, Commented Apr 30, 2020 at 20:38
I've added an expected output. Hope it's more clear now. You're solution works but not in the way I wanted to. Just adding [[ makes no changes. — Stefan
– Stefan, Commented Apr 30, 2020 at 20:52

akrun · Accepted Answer · 2020-04-30 21:03:18Z

1

Issue is that [ extraction is still a list with length one. So, we need to do [[. Also, if/else is not vectorized. Based on the updated OP's post, we need to check within each list elements. Here, if we stick with if/else, then a nested for loop is needed

for(i in seq_along(drop_rate)){
     tmp <- drop_rate[[i]]
     for(j  in 2:length(tmp)) {
          if(tmp[j-1] > tmp[j]) {
              tmp[j] <- tmp[j-1]
          }
         }
        drop_rate[[i]] <- tmp 


       }

We can use cummax

drop_rate <- lapply(drop_rate, cummax)
drop_rate
#$x1
#[1] 0.0000000 0.2666667 0.3466667 0.4666667 0.4666667 0.7333333

#$x2
#[1] 0.0000000 0.3076923 0.4102564 0.5000000 0.5000000 0.7307692

#$x3
#[1] 0.0000000 0.2763158 0.3815789 0.4736842 0.4736842 0.7368421

#$x4
#[1] 0.0000000 0.2987013 0.3896104 0.5064935 0.5064935 0.7402597

#$x5
#[1] 0.0000000 0.3116883 0.4025974 0.5064935 0.5064935 0.7272727

edited Apr 30, 2020 at 21:03

answered Apr 30, 2020 at 20:33

akrun

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1 Comment

Stefan Over a year ago

Works like a charm. And a lot more simpler. Thank you

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