Lookup/Find strings within a list of lists, and then return the list's name-CodePudding

I have a list of lists, like this example. For reference, my data has 300 lists each with around 90 components each, but of unequal length which is why it must stay in a list (I believe)

a <- list("FRUITS" = c("apples","bananas","pears"),
          "VEGGIES" = c("lettuce","pepper","carrot"),
          "BREADS" = c("bagel","muffin","sandwhich"))

and a dataframe that looks like this but has thousands of rows

b <- data.frame("Sample" = c("BB","TT","LT"),
        "Food" = c("SandWich","Tomato","BANANA"),
        "Volume" = c(124,1356,1343))

My goal is for my dataframe to mutate a new column that contains the list name that each Food item resides in. This is where Lookup/Finding strings within a list of lists and returning the list's name comes from.

data.frame("Sample" = c("BB","TT","LT"),
        "Food" = c("SandWich","Tomato","BANANA"),
        "Volume" = c(124,1356,1343),
        "Match" = c("BREADS","VEGGIES","FRUITS")

How can I do this? I have tried using other techniques on stack that around similar to Excel's VLOOKUP but no other threads are returning the lists' name from what I can tell.

Thanks for any help or feedback.

Edit: Case sensitivity

CodePudding user response：

In base R

transform(merge(b, stack(a), by.x = c("Food"), by.y = "values"),
    Food = ind, ind = NULL)

Or in tidyverse

library(tibble)
library(dplyr)
library(tidyr)
enframe(a, value = "Food") %>%
  unnest(Food) %>% 
  right_join(b, by = "Food") %>%
  mutate(Food = coalesce(name, Food), name = NULL)

If we need to change the case

library(purrr)
map(a, toupper) %>% 
  enframe(value = "Food") %>%
  unnest(Food) %>%
  right_join(b %>% 
     mutate(Food = toupper(Food)), by = "Food") %>% 
  mutate(Food = coalesce(name, Food), name = NULL)