How can I use `for loop` at once without non-numeric errors?-CodePudding

I wonder how for loop can be used at once without non-numeric error. I would like to make multiple character values in a vector Nums, using for loop.

But after the third line, the vector becomes chr so cannot continue the rest. This comes out to be same even when I use if loop or while loop... Can someone give a hint about this?

  for(n in 1:30){
    Nums<-1:n
    Nums[Nums%%2==0 & Nums%%3==0]<-"OK1"
    Nums[Nums%%2==0 & Nums%%3!=0]<-"OK2"
    Nums[Nums%%2!=0 & Nums%%3==0]<-"OK3"
    Nums[Nums%%2!=0 & Nums%%3!=0]<-n
  }

Error in Nums%%2 : non-numeric argument to binary operator

CodePudding user response：

I don't think the loop is actually doing what you want it to do. You are replacing Nums at every iteration, so nothing is actually being saved. Maybe you don't actually want a loop.

Nums <- 1:30
x <- 1:30

dplyr::case_when(
  Nums%%2==0 & x%%3==0 ~ "OK1",
  Nums%%2==0 & x%%3!=0 ~ "OK2",
  Nums%%2!=0 & x%%3==0 ~ "OK3",
  Nums%%2!=0 & x%%3!=0 ~ as.character(x)
)
#>  [1] "1"   "OK2" "OK3" "OK2" "5"   "OK1" "7"   "OK2" "OK3" "OK2" "11"  "OK1"
#> [13] "13"  "OK2" "OK3" "OK2" "17"  "OK1" "19"  "OK2" "OK3" "OK2" "23"  "OK1"
#> [25] "25"  "OK2" "OK3" "OK2" "29"  "OK1"

CodePudding user response：

Character and numeric values can't coexist in a vector^*. As @Ands. points out, you don't really need a loop for this. If you want to avoid case_when (which is from the dplyr package, part of the "tidyverse"), you can do:

n <- 30
Nums <- 1:n
x <- as.character(Nums)
x[Nums%%2==0 & Nums%%3==0]<-"OK1"
x[Nums%%2==0 & Nums%%3!=0]<-"OK2"
x[Nums%%2!=0 & Nums%%3==0]<-"OK3"

You don't need the final statement because the remaining elements were already set to the corresponding numeric values.

If you want to use a for loop and replace as you go, you could convert the vector to a list:

Nums <- 1:n
Nums <- as.list(Nums)
for (i in 1:n) {
   if (i%%2==0 & i%%3==0) Nums[[i]] <- "OK1"
   if (i%%2==0 & i%%3!=0) Nums[[i]] <- "OK2"
   if (i%%2!=0 & i%%3==0) Nums[[i]] <- "OK3"
}
unlist(Nums)

^* Technically they can't coexist in an atomic vector — lists are vectors too ...