how to merge two seperate histograms into one

Question

I have the following code:

library("ggplot2") 

x1 = as.numeric(x=QualidadeARO3$Ilhavo)
x2 = as.numeric(x=QualidadeARO3$VNTelha_Maia)

ggplot (QualidadeARO3, aes(x=x1, color="Ílhavo")) +
  geom_histogram(fill="black", position="dodge", alpha = 0.2) +
  theme(legend.position="top") + 
  xlab("microgramas por metro cúbico") + 
  ylab("horas") 

ggplot(QualidadeARO3, aes(x=x2, color="VN Telha-Maia")) +
  geom_histogram(fill="blue", position="dodge", alpha = 0.2)+
  theme(legend.position="top") +
  xlab("microgramas por metro cúbico") + 
  ylab("horas")

Where QualidadeARO3 is a data sheet imported from Excel that looks like this:

And

ggplot (QualidadeARO3, aes(x=x1, color="Ílhavo")) +
  geom_histogram(fill="black", position="dodge", alpha = 0.2) +
  theme(legend.position="top") + 
  xlab("microgramas por metro cúbico") + 
  ylab("horas")

gives the following ouput:

and

ggplot(QualidadeARO3, aes(x=x2, color="VN Telha-Maia")) +
  geom_histogram(fill="blue", position="dodge", alpha = 0.2)+
  theme(legend.position="top") +
  xlab("microgramas por metro cúbico") + 
  ylab("horas")

gives:

This is good and all so far, but my problem is that both graphs "run" independently, i.e., when I call the second ggplot the first graph disappears, when I want to overlap both into a single histogram, as well as both color labels. I have seen Overlaying histograms with ggplot2 in R , but still no clue. Any help?

@Quinten I can give you a link to it: https://docs.google.com/spreadsheets/d/1HfGKUktbU3dHLEOWhzUR_PS_kFUpy0RL/edit#gid=169599789 — A Burial At Ornans, May 12 '22 at 09:07
Copy the output of `dput(df)` and paste that in your question above please. — Quinten, May 12 '22 at 09:15

score 1 · Accepted Answer · answered May 12 '22 at 09:28

Try having separate geom layers like this:

ggplot (QualidadeARO3) +
  geom_histogram(aes(x=x1, color="Ílhavo", fill="Ílhavo"),
                 position="dodge", alpha = 0.2)+
  geom_histogram(aes(x=x2, color="VN Telha-Maia", fill="VN Telha-Maia"),
                 position="dodge", alpha = 0.2)+
  scale_fill_manual("Type", labels = c("Ílhavo", "VN Telha-Maia"),
                      values= c("black", "blue")) +
  scale_color_discrete("Type", labels = c("Ílhavo", "VN Telha-Maia")) +
  theme(legend.position="top") + 
  xlab("microgramas por metro cúbico") + 
  ylab("horas")

You can also use scale_fill_manual instead of scale_color_discrete if you want to have specific colors.

how to merge two seperate histograms into one

1 Answers1