(This article was first published on

**TRinker's R Blog » R**, and kindly contributed to R-bloggers)One of the most widely seen FAQ coming across list serves and R help sites is the question:

“How do I re-arrange/re-order (plotting geom/aesthetic such as bar/labels) in a (insert plot type here) using(insert graphics system here) in R?”

Don’t believe me? google “reorder factor r plot” and see how many hits you get. I’d venture to say that in almost all cases when you use the words “plot” and “re-arrange”/”re-order” in a question the answer is…

**Reorder your factor levels!!**

Here’s a quick and dirty R theater demo of how to do this:

library(ggplot2) ggplot(data=mtcars, aes(y=as.factor(carb), x=mpg, colour=hp)) + geom_point() # Rearrange_Guy: But I want 2 to come first and 8 last # Helpful_Gal: OK use rev with levels mtcars$carb2 <- factor(mtcars$carb, levels=rev(levels(factor(mtcars$carb)))) ggplot(data=mtcars, aes(y=carb2, x=mpg, colour=hp)) + geom_point() # Rearrange_Guy: Well I just want to specify the order # Helpful_Gal: OK type it in by hand then mtcars$carb2 <- factor(mtcars$carb, levels=c("1", "2", "3", "6", "8", "4")) ggplot(data=mtcars, aes(y=carb2, x=mpg, colour=hp)) + geom_point() # Rearrange_Guy: What about faceting? I bet it doesn't work for that. # Helpful_Gal: Um yes it does. ggplot(data=mtcars, aes(y=carb2, x=mpg, colour=hp)) + geom_point() + facet_grid(cyl~.) # Rearrange_Guy: OK Helpful_Gal I want it to go 6, 4, and then 8 # Helpful_Gal: OK mtcars$cyl2 <- factor(mtcars$cyl, levels=c("6", "4", "8")) ggplot(data=mtcars, aes(y=carb2, x=mpg, colour=hp)) + geom_point() + facet_grid(cyl2~.) # Rearrange_Guy: Why do you keep making new variables? # Helpful_Gal: It's probably not the best idea to overwrite variables just for the sake of plotting # Rearrange_Guy: Thank you for showing me the way of re-ordering and re-arranging. # Helpful_Gal: You welcome.

So if you catch yourself using “re-arrange”/”re-order” and “plot” in a question think…

factor & levels

To

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