How to combine member of a column, collect them in a data frame and give them a new name, in R?

I want to make a new data frame based on my old data frame and combine members of a specific column while I give them a new name:
for example, this is my old data frame:

df <- structure(list(ID= c("x1", "x1", "x1", "x1", "x1", "x1", "x2", "x2", "x2", "x2", "x2", "x2", "x3", "x3", "x3", "x3", "x3", "x3", "x1", "x1", "x1", "x1", "x1", "x1", "x2", "x2", "x2", "x2", "x2", "x2", "x3", "x3", "x3", "x3", "x3", "x3"),
col2= c("a", "b", "c", "d", "e", "f", "a", "b", "c", "d", "e", "f","a", "b", "c", "d", "e", "f","a", "b", "c", "d", "e", "f", "a", "b", "c", "d", "e", "f","a", "b", "c", "d", "e", "f"),
col3= c(2,13,1,21,0,5,3,0,6,4,50,0,0,0,0,9,5,0,51,3,6,0,0,9,89,4,29,1,4,17,6,16,9,1,0,0)), 
                class = "data.frame", row.names = c(NA,-36L))

and for the new dataframe I want to have a new column based on col2, so combine abc, where there is any of a or b or c, name it as abc.1. Combine de where there is d or e, name it as de.5 and finally where it is f name it as f.10. and for the new.col3 the SUM of their value in old col3.

The result would be:

df2<- structure(list(col1=c("a1","a1","a1","a2","a2","a2"),
new.col2= c("abc.1", "de.5", "f.10", "abc.1", "de.5", "f.10"),
                class = "data.frame", row.names = c(NA,-6L))

>Solution :

Create groups with case_when and then use summarise to collapse rows by groups and compute the sum of col3 by group.

df %>% 
  group_by(col1, gp = case_when(col2 %in% c("a", "b", "c") ~ 1,
                        col2 %in% c("d", "e") ~ 5,
                        col2 == "f" ~ 10)) %>% 
  summarise(new.col2 = paste(paste0(unique(col2), collapse = ""), unique(gp), sep = "."),
            new.col3 = sum(col3))


# A tibble: 6 × 4
# Groups:   col1 [2]
  col1     gp new.col2 new.col3
  <chr> <dbl> <chr>       <dbl>
1 a1        1 abc.1          25
2 a1        5 de.5           89
3 a1       10 f.10            5
4 a2        1 abc.1         213
5 a2        5 de.5            6
6 a2       10 f.10           26

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