Barplot of percentages by groups in ggplot2

So, I've done my searches but cannot find the solution to this problem i have with a bar plot in ggplot. I'm trying to make the bars be in percentage of the total number of cases in each group in grouping variable 2.

Right now i have it visualising the number of counts,

Dataframe = ASAP

Grouping variable 1 - cc_groups (seen in top of the graph) (counts number of cases within a range (steps of 20) in a score from 0-100.)

grouping variable 2 - asap ( binary variable with either intervention or control, number of controls and interventions are not the same)

Initial code

``` r
ggplot(ASAP, aes(x = asap, fill = asap)) + geom_bar(position = "dodge") + 
    facet_grid(. ~ cc_groups) + scale_fill_manual(values = c("red", 
    "darkgray"))
#> Error in ggplot(ASAP, aes(x = asap, fill = asap)): could not find function "ggplot"
```

^{Created on 2020-05-19 by the reprex package (v0.3.0)}

this gives me the following graph which is a visualisation of the counts in each subgroup.

enter image description here

I have manually calculated the different percentages that actually needs to be visualised:

table_groups <- matrix(c(66/120,128/258,34/120,67/258,10/120,30/258,2/120,4/258,0,1/258,8/120,28/258),ncol = 2, byrow = T)
colnames(table_groups) <- c("ASAP","Control")
rownames(table_groups) <- c("0-10","20-39","40-59","60-79","80-99","100")


         ASAP  Control
0-10  0.55000 0.496124
20-39 0.28333 0.259690
40-59 0.08333 0.116279
60-79 0.01667 0.015504
80-99 0.00000 0.003876
100   0.06667 0.108527

When i use the solution provided by Stefan below (which was an excellent answer but didn't do the actual trick. i get the following output

    ``` r
ASAP %>% count(cc_groups, asap) %>% group_by(cc_groups) %>% mutate(pct = n/sum(n)) %>% 
    ggplot(aes(x = asap, y = pct, fill = asap)) + geom_col(position = "dodge") + 
    facet_grid(~cc_groups) + scale_fill_manual(values = c("red", 
    "darkgray"))
#> Error in ASAP %>% count(cc_groups, asap) %>% group_by(cc_groups) %>% mutate(pct = n/sum(n)) %>% : could not find function "%>%"
```

<sup>Created on 2020-05-19 by the [reprex package](https://reprex.tidyverse.org) (v0.3.0)</sup>

enter image description here

whereas (when i go analogue) id like it to show the percentages as above like this.

enter image description here

Im SO sorry about that drawing.. :) and reprex kept feeding me errors, im sure im using it incorrectly.

Solution

The easiest way to achieve this is via aggregating the data before plotting, i.e. manually computing counts and percentages:

library(ggplot2)
library(dplyr)

ASAP %>% 
  count(cc_groups, asap) %>% 
  group_by(asap) %>% 
  mutate(pct = n / sum(n)) %>%   
  ggplot(aes(x = asap, y = pct, fill=asap)) + 
  geom_col(position="dodge")+
  facet_grid(~cc_groups)+
  scale_fill_manual(values = c("red","darkgray"))

Using ggplot2::mpg as example data:

library(ggplot2)
library(dplyr)

# example data
mpg2 <- mpg %>% 
  filter(cyl %in% c(4, 6)) %>% 
  mutate(cyl = factor(cyl))

# Manually compute counts and percentages
mpg3 <- mpg2 %>% 
  count(class, cyl) %>% 
  group_by(class) %>% 
  mutate(pct = n / sum(n)) 

# Plot 
ggplot(mpg3, aes(x = cyl, y = pct, fill = cyl)) +
  geom_col(position = "dodge") +
  facet_grid(~ class) +
  scale_fill_manual(values = c("red","darkgray"))

^{Created on 2020-05-18 by the reprex package (v0.3.0)}