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I want to recursively add text from one row to another using information stored in another column. Below is a sample dataset:

df <- data_frame(person = c(rep("A",4),rep("B",3)),
 meal = c(seq(1:4),seq(1:3)),
 food = c("Chicken", "Beef", "Soup and meal 2", "Lamb and meal 3",
 "Lamb","Salad and meal 1","Beef"),
 dependencies = c(NA,NA,2,3,NA,1,NA),
 solo_meal = c(1,1,0,1,1,0,1))

Which Gives:

# A tibble: 7 x 5
 person meal food dependencies solo_meal
 <chr> <int> <chr> <dbl> <dbl>
1 A 1 Chicken NA 1
2 A 2 Beef NA 1
3 A 3 Soup and meal 2 2 0
4 A 4 Lamb and meal 3 3 1
5 B 1 Lamb NA 1
6 B 2 Salad and meal 1 1 0
7 B 3 Beef NA 1

I want to add a column (preferably using tidyverse) that combines the food column to look like this:

 combined_meal 
 <chr> 
1 Chicken 
2 Beef 
3 Soup and Beef 
4 Lamb and Soup and Beef
5 Lamb 
6 Salad and Lamb 
7 Beef 

I am thinking that this needs to be done recursively, but I don't know how to do that in the tidyverse (or base for that matter).

Thanks for the help!

Here is a solution using a while loop.

library(dplyr)
library(stringr)
df <- data_frame(person = c(rep("A",4),rep("B",3)),
 meal = c(seq(1:4),seq(1:3)),
 food = c("Chicken", "Beef", "Soup and meal 2", "Lamb and meal 3",
 "Lamb","Salad and meal 1","Beef"),
 dependencies = c(NA,NA,2,NA,NA,1,NA),
 solo_meal = c(1,1,0,1,1,0,1))

df2 <- df %>% mutate(combined_meal = food)

while(any(grepl("meal",df2$combined_meal)))
 df2 <- df2 %>%
 group_by(person) %>%
 mutate(mls = str_extract(combined_meal,"\d"),
 f = combined_meal[strtoi(mls)],
 combined_meal = str_replace(combined_meal,"meal (\d)",f)) %>%
 select(-mls,-f) %>% 
 ungroup()

df2

#> # A tibble: 7 x 6
#> person meal food dependencies solo_meal combined_meal 
#> <chr> <int> <chr> <dbl> <dbl> <chr> 
#> 1 A 1 Chicken NA 1 Chicken 
#> 2 A 2 Beef NA 1 Beef 
#> 3 A 3 Soup and meal 2 2 0 Soup and Beef 
#> 4 A 4 Lamb and meal 3 NA 1 Lamb and Soup and Beef
#> 5 B 1 Lamb NA 1 Lamb 
#> 6 B 2 Salad and meal~ 1 0 Salad and Lamb 
#> 7 B 3 Beef NA 1 Beef

We can try this with accumulate

library(tidyverse)
map_df(split(df, df$person), function(x) 
 i = which(grepl('meal', x$food))
 i1 <- i[1] -1
 i2 <- i[length(i)]
 v1 <- x$food[i1:i2]
 v1 <- sub('and\s*$', "", 
 sub("meal\s+\d+", "", v1)) %>%
 accumulate(., c) %>%
 map_chr(~ .x %>% 
 rev %>% 
 paste(., collapse = ' and '))
 x$combined_meal <- x$food
 x$combined_meal[i1:i2] <- v1
 x)
# A tibble: 7 x 6
# person meal food dependencies solo_meal combined_meal 
# <chr> <int> <chr> <dbl> <dbl> <chr> 
#1 A 1 Chicken NA 1 Chicken 
#2 A 2 Beef NA 1 Beef 
#3 A 3 Soup and meal 2 2 0 Soup and Beef 
#4 A 4 Lamb and meal 3 NA 1 Lamb and Soup and Beef
#5 B 1 Lamb NA 1 Lamb 
#6 B 2 Salad and meal 1 1 0 Salad and Lamb 
#7 B 3 Beef NA 1 Beef