Suppose you have an EEG dataset where every column is an electrode E1....E129.

First, you want to compute the spatial standard deviation GFP. How would you rewrite rowSD using dplyr rowwise? Next you want to normalize each electrode by dividing it with GFP. What goes into the mutate_all? Thanks!

```
library(dplyr)
library(RFunctionsSN)
tibble(E1 = rnorm(10), E2 = rnorm(10), E3 = rnorm(10), E4 = rnorm(10)) %>%
mutate(GFP = rowSD(.)) %>%
mutate_all()
```