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"),
col1=c("a1","a1","a1","a1","a1","a1","a1","a1","a1","a1","a1","a1","a1","a1","a1","a1","a1","a1","a2","a2","a2","a2","a2","a2","a2","a2","a2","a2","a2","a2","a2","a2","a2","a2","a2","a2"),
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"),
new.col3=c(25,89,5,213,6,26)),
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.

```
library(dplyr)
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))
```

output

```
# 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
```