Changing the order of categories shown in conditional effects plots brms

Interfaces brms
#1

Short summary of the problem

I am running a simple logistic regression with an interaction between between two categorical variables, one with five categories and the other binary. The conditional_effects() command displays the bars for the reference category first, but I want to change the order that the bars appear. Is there a way to do that?

code_to_run_your_model(if_applicable)

fit <- brms(y ~ x1*x2, family=‘bernoulli’, data=dat)
conditional_effects(fit,“x1:x2”)

x1 has five levels, (0, 1, 2, 3, 4), and the reference category is 2. Currently, the bars are plotted in the order of 2 0 1 3 4. I would like to have them shown from 0 to 4. Is this possible without having to change the reference category to 0?

Thank you

Please also provide the following information in addition to your question:

  • Operating System: Windows 10
  • brms Version: 2.12.0

Looking forward to your topic!

#2

One relatively easy way to do this is to save the plot as an object and change the order of the levels directly in the plot object:

# save plot as p
p <- conditional_effects(fit,“x1:x2”)

#change order of factor levels in plot
p$`x1:x2`$effect1__ <- factor(p$`x1:x2`$effect1__, levels(p$`x1:x2`$effect1__)[c(2,3,1,4,5)])

#plot again
p

should do what you want. I hope this answers your question.

If you wanted to do the same thing for the main-effect plot of x1 the 2nd line would become

p$x1$effect1__ <- factor(p$x1$effect1__, levels(p$x1$effect1__)[c(2,3,1,4,5)])
#3

That worked! Thanks a lot!