Nested list into data frame

I have not found an example that applies to my specific problem, but feel free to label as duplicate if needed.

I have a nested list like the following:

nested_list <- list(
  ID1 = list(
    FEAT = list(
      feat1 = list(start = "1", end = "15", label = "CDR1"),
      feat2 = list(start = "20", end = "25", label = "CDR2")
    ),
    SEQ = "ACTGATCGTAGCTAGCTAGATGCTGATGTGTC"
  ),
  ID2 = list(
    SEQ = "ACTGATCGGCGGTGGCTAGCTGTGGGGCGCGCGACCGGGAAAA"
  )
)

I want to obtain a data frame like this:

   id  feat feat_label feat_start feat_end                                    full_seq
1 ID1 feat1       CDR1          1       15            ACTGATCGTAGCTAGCTAGATGCTGATGTGTC
2 ID1 feat2       CDR2         20       25            ACTGATCGTAGCTAGCTAGATGCTGATGTGTC
3 ID2  <NA>       <NA>         NA       NA ACTGATCGGCGGTGGCTAGCTGTGGGGCGCGCGACCGGGAAAA

as.data.frame(nested_list) does not produce what I want, so it probably needs an extra step to turn the data frame into "longer" format, ideally with something like tidyr::pivot_longer().

I think this gets you the essentials of what you want. The column order and column names are easily adjusted.

nested_list <- list(
  ID1 = list(
    FEAT = list(
      feat1 = list(start = "1", end = "15", label = "CDR1"),
      feat2 = list(start = "20", end = "25", label = "CDR2")
    ),
    SEQ = "ACTGATCGTAGCTAGCTAGATGCTGATGTGTC"
  ),
  ID2 = list(
    SEQ = "ACTGATCGGCGGTGGCTAGCTGTGGGGCGCGCGACCGGGAAAA"
  )
)
library(purrr)

Unpack2 <- function(L) {
  map_dfr(L, .f = \(Row) unlist(Row))
}

Unpack1 <- function(NAME) {
  LIST <- nested_list[[NAME]]
  if(!is.null(LIST$FEAT)) {
    tmp <- LIST$FEAT
    Nms <- names(tmp)
    DF <- Unpack2(tmp)
    DF$feat <- Nms
  } else {
    DF <- data.frame(start = NA, end = NA, label = NA)
  }
  DF$ID <- NAME
  DF$Seq <- LIST$SEQ
  return(DF)
}

ListNames <- names(nested_list)
map_dfr(ListNames, Unpack1)
#> # A tibble: 3 × 6
#>   start end   label feat  ID    Seq                                        
#>   <chr> <chr> <chr> <chr> <chr> <chr>                                      
#> 1 1     15    CDR1  feat1 ID1   ACTGATCGTAGCTAGCTAGATGCTGATGTGTC           
#> 2 20    25    CDR2  feat2 ID1   ACTGATCGTAGCTAGCTAGATGCTGATGTGTC           
#> 3 <NA>  <NA>  <NA>  <NA>  ID2   ACTGATCGGCGGTGGCTAGCTGTGGGGCGCGCGACCGGGAAAA

^{Created on 2024-11-25 with reprex v2.1.1}