double for loop with an if condition

[Hassanhijazi]

I am wondering what is the problem here?
I need the output as follows:

"a*" "b" "c*" "d" "e*"

data1 <- c("a", "b", "c", "d", "e")
data2 <- c("a", "c", "e")
for (i in data1){
for (j in data2){
if_else(i == j, paste0(data1[i], "*"),
data1[i])
}

}

data1

data1
[1] "a" "b" "c" "d" "e"

[FactOREO]

Hello,

you have the following problem: Your index i and j are along your vector entries, not the positions. This will work without an error:

library(dplyr)
#> 
#> Attache Paket: 'dplyr'
#> Die folgenden Objekte sind maskiert von 'package:stats':
#> 
#>     filter, lag
#> Die folgenden Objekte sind maskiert von 'package:base':
#> 
#>     intersect, setdiff, setequal, union
data1 <- letters[1:5]
data2 <- c("a", "c", "e")
for (i in seq_along(data1)){
  for (j in seq_along(data2)){
    if_else(data1[[i]] == data2[[j]],
            paste0(data1[[i]], "*"),
            data1[[i]])
  }
}

^{Created on 2022-08-20 by the reprex package (v2.0.1)}

If you wish to keep the result, you have to define a variable which allows replacement (e.g. replace inside data1 with data1[[i]] <- or define a new variable).

library(dplyr)
#> 
#> Attache Paket: 'dplyr'
#> Die folgenden Objekte sind maskiert von 'package:stats':
#> 
#>     filter, lag
#> Die folgenden Objekte sind maskiert von 'package:base':
#> 
#>     intersect, setdiff, setequal, union
data1 <- letters[1:5]
data2 <- c("a", "c", "e")
for (i in seq_along(data1)){
  for (j in seq_along(data2)){
    data1[[i]] <- if_else(data1[[i]] == data2[[j]],
            paste0(data1[[i]], "*"),
            data1[[i]])
  }
}

data1
#> [1] "a*" "b"  "c*" "d"  "e*"

^{Created on 2022-08-20 by the reprex package (v2.0.1)}

Kind regards

[Hassanhijazi]

Hello @FactOREO,

Thank you for your reply. It works perfectly. I just wonder, as you said, if I want to capture the new generated data in a vector other than data1, how could it work then ?

I tried to add outside the for loop an empty vector (data3 <- c()) then replace inside the for loop:
data1[[i]] withdata3[[i]], but it didn't work.

Thank you in advance.

[FactOREO]

Yes, this cannot work indeed. But since you know the dimension of the new vector (here 5), you can create an empty vector with length 5 beforehand. This way you won't get any 'subscript out of bounds' error. Just add my_results_vector <- vector(length=5) in front of the loop and then asign the value to my_results_vector[[i]].

[Hassanhijazi]

Super. Thank you again.