Data wrangling: Aggregating by group sequentially reducing

Question

I'm newbie to R. I need to aggregate the data by group with sequence. I'm adding my data frame. first two column is given data, I have to mutate third column.

df <- data.frame(id = c(rep("a",3), rep("b",2), rep("c", 4)),
               value = c("x", "z", "p", "q", "q", "m", "n", "x", "y"), 
               reqd = c("x,z,p", "z,p", "p", "q,q","q", "m,n,x,y", "n,x,y", "x,y", "y"))

I had aggregated by group but its not correct

df_2 <- df[,1:2]  %>% 
group_by(id) %>% 
mutate(reqd2 = paste(value, collapse = ","))

Answer 1

We can group_by id and create a sequence between current row_number and total number of rows in each group and concatenate the corresponding value with toString.

library(dplyr)
library(tidyr)

df %>%
  group_by(id) %>%
  mutate(reqd1 = map2_chr(row_number(),n(),~toString(value[.x:.y])))

#  id    value reqd    reqd1     
#  <fct> <fct> <fct>   <chr>     
#1 a     x     x,z,p   x, z, p   
#2 a     z     z,p     z, p      
#3 a     p     p       p         
#4 b     q     q,q     q, q      
#5 b     q     q       q         
#6 c     m     m,n,x,y m, n, x, y
#7 c     n     n,x,y   n, x, y   
#8 c     x     x,y     x, y      
#9 c     y     y       y        

---

We can also do this using only base R with ave

with(df, ave(value, id, FUN = function(x) 
        mapply(function(i, j) toString(x[i:j]), seq_along(x), length(x))))

#[1] "x, z, p"  "z, p"  "p"  "q, q"   "q"   "m, n, x, y"  "n, x, y"  "x, y" "y"