Order of factor levels changes when plotting layers with data subsets

Question

I am trying to control the order of items in a legend in a `ggplot2` plot in R. I looked up some other similar questions and found out about changing the order of the levels of the factor variable I am plotting. I am plotting data for 4 months, December, January, July, and June. If I just do one plot command for all the months, it works as expected with the months ordered in the legend appearing in the order of the levels of the factor. However, I need to have a different `dodge` value for the summer (June & July) and winter (Dec & Jan) data. I do this with two `geom_pointrange` commands. When I divide it into 2 steps, the order of the legend goes back to alphabetical. You can demonstrate by commenting out the "plot summer" or "plot winter" command. What can I change to keep my factor level order in the legend? Please ignore the odd looking test data - the real data looks fine in this plot format. ``` #testdata hour <- rep(seq(from=1,to=24,by=1),4) avg_hou <- sample(seq(0,0.5,0.001),9…

Accepted Answer

Another way to think about "dodge" is as an offset from the x-values based on group (in this case Month). So if we add a dodge (x-offset) column to your original data, based on month:

```
# your original sample data
# note the use of set.seed(...) so "random" data is reproducible
set.seed(1)
hour     <- rep(seq(from=1,to=24,by=1),4)
avg_hou  <- sample(seq(0,0.5,0.001),96,replace=TRUE)
lower_ci <- avg_hou - sample(seq(0,0.05,0.001),96,replace=TRUE)
upper_ci <- avg_hou + sample(seq(0,0.05,0.001),96,replace=TRUE)
Month    <- c(rep("December",24), rep("January",24), rep("June",24), rep("July",24))
testdata       <- data.frame(Month,hour,avg_hou,lower_ci,upper_ci)
testdata$Month <- factor(testdata$Month,levels=c("June", "July", "December","January"))

# add offset column for dodge
testdata$dodge <- -2.5+(as.integer(testdata$Month))

# create ggplot object and default mappings
ggp <- ggplot(testdata, aes(x=hour, y = avg_hou, ymin = lower_ci, ymax = upper_ci, color = Month, shape = Month))
ggp <- ggp + scale_color_manual(values = c("June" = "#FDB863", "July" = "#E66101", "December" = "#92C5DE", "January" = "#0571B0"))

# plot the point range
ggp + geom_pointrange(aes(x=hour+0.2*dodge), size=1)
```

Produces this:

This does not require `geom_blank(...)` to maintain the scale order, and it does not require two calls to `geom_pointrange(...)`

Order of factor levels changes when plotting layers with data subsets

Solution

Problem