How can I select specific items in a list that are not at the top level?

Question

I'm trying to select specific items in a list that are not in the top level, and everything I can think of doesn't work the way I would expect. Here is a dummy list where what I do NOT want is item "C":

MyList <- list("pine" = list(A = data.frame(), 
                             B = data.frame(), 
                             C = hist(rnorm(10))), 
               "fir" = list(A = data.frame(), 
                            B = data.frame(), 
                            C = hist(rnorm(10))), 
               "cedar" = list(A = data.frame(), 
                              B = data.frame(), 
                              C = hist(rnorm(10))))

If I only needed to go one level down, this is what I would do to get only "A" and "B":

MyList[["pine"]][c("A", "B")]

I thought that one of these two approaches would mimic that, but both give me errors:

NotC <- map(.x = MyList, 
        .f = \(x) map(x, .f = x[c("A", "B")]))

NotC <- lapply(MyList, \(x) lapply(x, \(y) y[c("A", "B")]))

It seems that R thinks I'm trying to select columns, because I'm getting errors such as "Error in `[.data.frame`(y, c("A", "B")) : undefined columns selected"

Answer 1

If it is always called "C" you can do this.

MyList <- list("pine" = list(A = data.frame(), 
                             B = data.frame(), 
                             C = hist(rnorm(10))), 
               "fir" = list(A = data.frame(), 
                            B = data.frame(), 
                            C = hist(rnorm(10))), 
               "cedar" = list(A = data.frame(), 
                              B = data.frame(), 
                              C = hist(rnorm(10))))

deletec <- function(l) {
  l[names(l) != "C"]
}

lapply(MyList, deletec)
> $pine $pine$A data frame with 0 columns and 0 rows
> 
> $pine$B data frame with 0 columns and 0 rows
> 
> 
> $fir $fir$A data frame with 0 columns and 0 rows
> 
> $fir$B data frame with 0 columns and 0 rows
> 
> 
> $cedar $cedar$A data frame with 0 columns and 0 rows
> 
> $cedar$B data frame with 0 columns and 0 rows

You could write it more compactly, but basically write a function that does what you want. Then lapply() that function.