Search code examples
rggplot2facet

ggplot2 facet labels don't correspond to data

I'm an R newbie and I'm probably missing something trivial, but here it goes:

I have a data frame Data with values like so:

         Voltage Current  lnI     VoltageRange
    1    0.474   0.001 -6.907755  Low Voltage
    2    0.883   0.002 -6.214608  Low Voltage
    3    1.280   0.005 -5.298317  Low Voltage
    .      .       .        .          .
    .      .       .        .          .
    .      .       .        .          .
    .      .       .        .          .
   13    2.210   0.247 -1.398367 High Voltage

Then I try to plot it with the following code:

ggplot(data = Data, mapping = aes(x = Data$lnI, y = Data$Voltage)) +
      geom_point() +
      stat_smooth(method = "lm", se = FALSE) +
      facet_grid(~VoltageRange)

The output of which is: enter image description here

As you can see, the facet labels are in the wrong place, what is labeled as High voltage corresponds to low voltage and vice versa.

How do I go about fixing this? What am I doing wrong?

Solution

  • As commented. I think your ggplot call is 'too complicated'

    require(read.so) #awesome package available on GitHub, by @alistaire47 
dat <- read_so() 
dat <- dat[c(1:3,8),] 

dat
# A tibble: 4 x 4
  Voltage Current lnI       VoltageRange
  <chr>   <chr>   <chr>     <chr>       
1 0.474   0.001   -6.907755 Low         
2 0.883   0.002   -6.214608 Low         
3 1.280   0.005   -5.298317 Low         
4 2.210   0.247   -1.398367 High 

ggplot(dat, aes(x = lnI, y = Voltage)) + # remove 'mapping', 
# and use only the object names, not the columns/ vectors
  geom_point() + 
  stat_smooth(method = "lm", se = FALSE) +
  facet_grid(~VoltageRange)

    works: enter image description here

    edit If you want to re-arrange the facet, factorise the argument and change the order of the levels. You can do this in the data frame (which I would not recommend) or in the ggplot call directly. In order to do so, I find it good to create a character vector with the order of the levels, because you might need this one again. 

    facet_order <- c('Low', 'High') 
# note it's important that the levels are written exactly the same
ggplot(dat, aes(x = lnI, y = Voltage)) + 
      stat_smooth(method = "lm", se = FALSE) +
      facet_grid(~factor(VoltageRange, levels = facet_order))