With {dplyr} and {purrr} I would like to calculate the sum of each numerical column that begins with "eff".

```
library(dplyr)
library(purrr)
mydf <- tribble(
~categ_21, ~categ_22, ~eff_21, ~eff_22,
"a", "b", 1, 5,
"b", "b", 2, 6,
"c", "c", 3, 7,
"c", "a", 4, 8
)
```

What I want :

```
result <- tribble(
~categ, ~eff_21, ~eff_22,
"a", 1, 8,
"b", 2, 11,
"c", 7, 7
)
```

I tried but it creates several data.frames and it is long, that’s why I want to use {purrr} because in my real working data.frame I have more columns than "21" and "22" :

```
mydf %>%
group_by(categ_21) %>%
summarise(total_21 = sum(eff_21))
mydf %>%
group_by(categ_22) %>%
summarise(total_22 = sum(eff_22))
```

Thanks!

### >Solution :

In this particular case, you may find it convenient to pivot long, and then back to wide:

```
library(dplyr)
library(tidyr)
mydf %>%
pivot_longer(everything(),names_to = c(".value", "cat"), names_pattern="(.*)_(.*)") %>%
pivot_wider(categ,names_from = cat,values_from = eff, values_fn = sum,names_prefix = "eff_")
```

Output:

```
categ eff_21 eff_22
<chr> <dbl> <dbl>
1 a 1 8
2 b 2 11
3 c 7 7
```