Calling a list index within a loop using names() - r

Question

I have a list aa which references the index names of another list bb as well as containing one other element (call it cm). List bb items contain strings. I have a loop that goes through bb and, for every item which matches a string I've specified, adds it to a new row in a dataframe. What I need is to also add the cm value to that row.
Example:
library("tidyverse")
aa <- list(c(123, 1), c(234, 1), c(345, 2), c(456, 3))
bb <- list("123" = c("a", "b", "c"), "234" = c("b", "c", "d"), "345" = c("c", "d", "e"), "456" = c("f", "g", "h"))
cc <- c("a", "b", "c")
tbl <- NULL
for (a in aa){
for (b in bb) {
if (any(cc %in% b)) {
tb <- tibble(cm=a[2],n1=b[1],n2=b[2],n3=b[3])
tbl <- bind_rows(tbl,tb)
}
}
}
This iterates through for every possible combination of bb, and adds it to pairs it to every cm, which is no good. My output should look something like this:
output <- tibble(cm = c(1, 1, 2), n1 = c("a", "b", "c"),
n2 = c("b", "c", "d"), n3 = c("c", "d", "e"))
> output
# A tibble: 3 x 4
cm n1 n2 n3
<dbl> <chr> <chr> <chr>
1 1 a b c
2 1 b c d
3 2 c d e
I thought maybe something like this would work, as at least then I could loop through tbl later and use nm to replace it with the appropriate cm values:
tbl <- NULL
for (a in aa){
for (b in bb) {
if (any(cc %in% b)) {
tb <- tibble(nm = names(bb)[b], n1=b[1],n2=b[2],n3=b[3])
tbl <- bind_rows(tbl,tb)
}
}
}
I don't really understand why this doesn't work, because names(bb)[1] returns 123 so I figured it would work the same in a loop with names(bb)[b].

Answer 1

If you're happy with a base R solution without the explicit loops, would this work?
# generate data
aa <- list(c(123, 1), c(234, 1), c(345, 2), c(456, 3))
# cm is an element of bb
bb <- list("123" = c("a", "b", "c"), "234" = c("b", "c", "d"),
"345" = c("c", "d", "e"), "456" = c("f", "g", "h"),
cm = c(1, 1, 2))
cc <- c("a", "b", "c")
tbl <- data.frame(
bb[["cm"]],
# apply to each element of aa
do.call(rbind, lapply(aa, function(x, y, c) { # function takes 3 args
# only elements of bb whose names are in aa[[x]]
names_y <- as.character(intersect(x, names(y)))
# turn subset of bb into data.frame
out <- as.data.frame(do.call(rbind, y[names_y]))
# subset rows for which any row element %in% cc
out <- out[apply(out, 1, function(x, c) any(x %in% c), c)]
return(out)
}, bb, cc))) # pass bb and cc as args to the function in lapply()
names(tbl) <- c("cm", paste0("n", 1:(ncol(tbl) - 1)))
gives
> tbl
cm n1 n2 n3
123 1 a b c
234 1 b c d
345 2 c d e