ggplot2: How to manually fix the order in which bars appear

Question

I am plotting and saving multiple plots using ggplot in a for loop, which loops through a list. Sample list elements look like this:

head(genes[[1]])

name              fc                  fdr
gene1         -2.0143529             0.0002
protein1      -3.2256188             0.0001

I used the following code to plot:

p<-list()
for(i in 1:length(genes)){
p[[i]]<-ggplot(genes[[i]], aes(name,fc, label= name))+
geom_col(aes(fill=factor(fdr < 0.05)), position = "dodge", width = 1)+
coord_flip()+scale_fill_manual(values = c("#00BFC4","#F8766D"))

Omitting the additional code that deals with formatting. The final plots looks like this:

Now, the problem is that I am plotting over a 100 of these plots using the for loop and I would like to always keep the gene (first row in the list element) to be the top bar and the protein to be the bottom bar since I have omitted all labels and plan to use a single legend for all the plots. However, ggplot keeps switching the order of the bars among different plots. Is there a way to make sure that that doesn't happen and the gene always stays on top? Thanks, Shash

Jeremy Voisey Jeremy Voisey · Accepted Answer · 2017-04-21T10:53:51

ggplot will order the bars alphabetically by name.

For example

library(ggplot2)

df <- data.frame(name = c("A-gene", "B-protein"), fc = c(-2.2, -3.2), fdr = c(0.2, 0.003))

ggplot(df, aes(name,fc, label= name))+
    geom_col(aes(fill=factor(fdr < 0.05)), position = "dodge", width = 1)+
    coord_flip()+scale_fill_manual(values = c("#00BFC4","#F8766D"))
dev.off()

To get the bars in the order you require, make the name variable a factor, and set the order of levels. With just two names, you can use relevel as follows

library(ggplot2)
df <- data.frame(name = c("A-gene", "B-protein"), fc = c(-2.2, -3.2), fdr = c(0.2, 0.003))

df$name <- relevel(df$name, as.character(df$name[2])) 

ggplot(df, aes(name,fc, label= name))+
    geom_col(aes(fill=factor(fdr < 0.05)), position = "dodge", width = 1)+
    coord_flip()+scale_fill_manual(values = c("#00BFC4","#F8766D"))
dev.off()

This makes the second row (protein) the bar next to the origin.

ggplot2: How to manually fix the order in which bars appear

1 Answers