How can I lapply to sub element of list within a list

Question

Suppose I have a list nested within a list and I have some function which only works on vectors (like str_replace from the stringr package). The function should do its work on every element which actually entails information, ... Question 1: Is there a specific solution to my problem? Question 2: Is there a general solution? There should be a solution using loops, but that is all but elegant and probably very slow - efficiency does play a role here. Let's have an example: ``` # let's start easy: test1 <- list(c("a","d"),c("b","d"),c("c","d")) # does not work: str_replace(test1,"d","changed") # but this does: lapply(test1,str_replace,"d","changed") # but what now ? test2 <- list(c(list("a"),"d"),c("b","d"),c("c","d")) # does not work! :-( lapply(test2,str_replace,"d","changed") ```

Accepted Answer

You can use `unlist`/`relist`:

```
library(stringr)
test <- list(c(list("a"),"d"),c("b","d"),c("c","d"))
test2 <- unlist(test)
test2 <- str_replace(test2,"d","changed")
relist(test2,test)

[[1]]
[[1]][[1]]
[1] "a"

[[1]][[2]]
[1] "changed"

[[2]]
[1] "b"       "changed"

[[3]]
[1] "c"       "changed"
```

I believe this is pretty efficient, but have not tested.

How can I lapply to sub element of list within a list

Solution

Problem