How to check which element of a list which is a logical list is TRUE in R?

To check which element of a list which is a logical list is TRUE, we can follow the below steps −

• First of all, create a list with logical values.
• Use which function with unlist function to find the position of TRUE elements.

Create the list

Let’s create a list as shown below −

List<-
list(TRUE,FALSE,TRUE,TRUE,FALSE,FALSE,FALSE,TRUE,FALSE,TRUE,FALSE,FALSE,TRUE,TRUE,TRUE,TRUE,FALSE,TRUE,FALSE,FALSE,TRUE,FALSE,TRUE,FALSE,TRUE)
List

On executing, the above script generates the below output(this output will vary on your system due to randomization) −

[[1]]
[1] TRUE

[[2]]
[1] FALSE

[[3]]
[1] TRUE

[[4]]
[1] TRUE

[[5]]
[1] FALSE

[[6]]
[1] FALSE

[[7]]
[1] FALSE

[[8]]
[1] TRUE

[[9]]
[1] FALSE

[[10]]
[1] TRUE

[[11]]
[1] FALSE

[[12]]
[1] FALSE

[[13]]
[1] TRUE

[[14]]
[1] TRUE

[[15]]
[1] TRUE

[[16]]
[1] TRUE

[[17]]
[1] FALSE

[[18]]
[1] TRUE

[[19]]
[1] FALSE

[[20]]
[1] FALSE

[[21]]
[1] TRUE

[[22]]
[1] FALSE

[[23]]
[1] TRUE

[[24]]
[1] FALSE

[[25]]
[1] TRUE

Find the position of TRUE elements

Unlist of the List elements and use which function to find which elements are TRUE in List −

List<-
list(TRUE,FALSE,TRUE,TRUE,FALSE,FALSE,FALSE,TRUE,FALSE,TRUE,FALSE,FALSE,TRUE,TRUE,TRUE,TRUE,FALSE,TRUE,FALSE,FALSE,TRUE,FALSE,TRUE,FALSE,TRUE)
< which(unlist(List))

Output

[1] 1 3 4 8 10 13 14 15 16 18 21 23 25

Nizamuddin Siddiqui

Updated on: 13-Aug-2021

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