R – Avoid ggplot sorting the x-axis while plotting geom_bar()

ggplot2r

I have the following data which I want to plot with ggplot:

SC_LTSL_BM    16.8275
SC_STSL_BM    17.3914
proB_FrBC_FL   122.1580
preB_FrD_FL    18.5051
B_Fo_Sp    14.4693
B_GC_Sp    15.4986

What I want to do is to make a bar plot and maintain the order of the bar,
(i.e. starting with SC_LTSL_BM ...B_GC_Sp). But the default behavior of
ggplot geom_bar is to sort them. How can I avoid that?

  library(ggplot2)
  dat <- read.table("http://dpaste.com/1469904/plain/")
  pdf("~/Desktop/test.pdf")
  ggplot(dat,aes(x=V1,y=V2))+geom_bar()
  dev.off()

The current figure looks like this:
enter image description here

Best Answer

You need to tell ggplot that you've got an ordered factor already, so it doesn't automatically order it for you. 

dat <- read.table(text=
"SC_LTSL_BM    16.8275
SC_STSL_BM    17.3914
proB_FrBC_FL   122.1580
preB_FrD_FL    18.5051
B_Fo_Sp    14.4693
B_GC_Sp    15.4986", header = FALSE, stringsAsFactors = FALSE)

# make V1 an ordered factor
dat$V1 <- factor(dat$V1, levels = dat$V1)

# plot
library(ggplot2)
ggplot(dat,aes(x=V1,y=V2))+geom_bar(stat="identity")

enter image description here

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