Divide all columns by a chosen column using mutate_all

UPDATE to answer by @arg0naut91 (dplyr 1.0.0)

Example_Ratio <- example %>% 
  mutate(across(everything()), . / Zr) %>% 
  select(Ratio_Elements)

Something like this perhaps:

library(tidyverse)

d <- seq(0, 100, 0.5) 
Fe <- runif(201, min = 0, max = 1000) 
Ca <- runif(201, min = 0, max = 1000) 
Zr <- runif(201, min = 0, max = 1000) 
Ti <- runif(201, min = 0, max = 1000) 
Al <- runif(201, min = 0, max = 1000) 
example <- data.frame(d, Fe, Ca, Zr, Ti, Al)
Ratio_Elements <- c("Fe", "Ti", "Zr", "d") #this subset of the 

Example_Ratio <- example %>%
  mutate_at(vars(-Zr), funs(. / Zr)) %>%
  select(Ratio_Elements)

I know you said you'd like to see a mutate_all solution, but I guess you don't want to divide Zr by itself?

In this case mutate_at is more helpful, otherwise you can do mutate_all(funs(. / Zr)).

If you want to keep the mentioned vector:

Detrital_Divisor <- as.symbol("Zr")

Example_Ratio <- example %>%
  mutate_at(vars(- !! Detrital_Divisor), funs(. / !! Detrital_Divisor)) %>%
  select(Ratio_Elements)

---

UPDATE (dplyr 0.8.0)

Now that funs is deprecated as of dplyr 0.8.0, you can just use ~, e.g.:

Detrital_Divisor <- as.symbol("Zr")

Example_Ratio <- example %>%
  mutate_at(vars(- !! Detrital_Divisor), ~ . / !! Detrital_Divisor) %>%
  select(Ratio_Elements)

On the other hand there's also list - useful for mutating in multiple ways or naming the output, e.g.:

Example_Ratio <- example %>%
  mutate_at(vars(- !! Detrital_Divisor), list(appended_name = ~ . / !! Detrital_Divisor))

---

UPDATE (dplyr 1.0.0)

As of dplyr 1.0.0, you would probably want to use across:

Example_Ratio <- example %>%
  mutate(across(-Detrital_Divisor, ~ . / !! Detrital_Divisor)) %>%
  select(all_of(Ratio_Elements))