I have disease scores for a lot of trees with % dieback/ infection readings taken in two consecutive years. I can create a histogram in ggplot2 in r for each year, but how do I create a side-by-side bar plot showing the readings for each year side by side with ranges e.g. 0-10, 10-20, 20-30% up to 100% infection on the x axis?

I create a simple dataframe with two readings for each year:

diseaseyear1 <- c(20, 30, 40, 50, 30, 20, 60, 85, 45, 32, 20, 40)
diseaseyear2 <- c(30, 35, 42, 45, 25, 70, 65, 90, 40, 25, 35, 50)
totaldisease <- tibble(diseaseyear1, diseaseyear2)
totaldisease
#I can plot year 1
quartz(10, 5)
year1 <- ggplot(totaldisease)  
  aes(x=diseaseyear1)  
  geom_histogram(binwidth = 10)  
  labs(title = "Disease Year 1",
       y = "count", x = "% of disease")  
  theme(text = element_text(size = 10, family = "GillSans"))
#I can also plot year 2
year1 <- ggplot(totaldisease)  
  aes(x=diseaseyear1)  
  geom_histogram(binwidth = 10)  
  labs(title = "Disease Year 1 & 2",
       y = "count", x = "% of disease")  
  theme(text = element_text(size = 10, family = "GillSans"))

#but how can I combine these two histograms (or bar plots) as side by side bars in one chart?

CodePudding user response：

We need to first convert our data to a long format. This way, we can better plot the data.

 totaldisease %>% 
  tidyr::pivot_longer(names_to = "dis", values_to = "val",
                      cols = 1:ncol(.)) %>% 
  ggplot(aes(val, fill=dis)) 
  geom_histogram(binwidth = 10) 
  labs(title = "Disease Year 1 & 2",
       y = "count", x = "% of disease")  
  theme(text = element_text(size = 10, family = "GillSans"))

Result

If you need it dodged

totaldisease %>% 
  tidyr::pivot_longer(names_to = "dis", values_to = "val",
                      cols = 1:ncol(.)) %>% 
  ggplot(aes(val, fill=dis)) 
  geom_histogram(binwidth = 10, position = "dodge") 
  labs(title = "Disease Year 1 & 2",
       y = "count", x = "% of disease")  
  theme(text = element_text(size = 10, family = "GillSans"))