R: Order of points and lines within geom in ggplot2 - r

Question

I am trying to plot a dataframe in ggplot and am having trouble getting the points and lines to display in the desired order.
The data is split based on the same column (of factors 0 or 1) and I want 0 to plot over 1 for both lines and points (which use data from 4 other separate columns).
I have made a test data frame below to illustrate my point. My real dataframe has thousands of points, and I want to plot a number of dataframes so don't really want to use a work around like subsetting my data and plotting as separate layers/geoms.
testdata <- data.frame(Split = c(rep(0,5), rep(1,5)), a = rep(1:5,2),
b = c(7,8,9,10,11,6,8,9,10,12), x = c(1:5, 1:5), y = c(1:3,5,6,1.1,2.1,4.1,5.1,7.1))
testdata$Split <- factor(testdata$Split)
ggplot(data = testdata)+
geom_point(aes(x = x, y = y, colour = Split), size = 4)+
geom_line(aes(x = a, y = b, colour = Split))
testdata$Split <- ordered(testdata$Split, levels = rev(levels(testdata$Split)))
When i run the line of code to reverse the order of my levels, it swaps which of my lines is brought to the front, but not which set of points. So initially both the points and line relating to Split = 0 are behind, however when I reverse the order the line from Split = 0 is infront (what I want) but the points for Split = 0 remain behind the points for Split = 1.
Any idea what's going on here and how I can get this to work would be appreciated.
Thanks

Answer 1

After investigating the situation for some time, this is what I found and suggest. In short, I believe that the solution is to assign the value 2 to 0 in unclass().
foo <- data.frame(split = rep(c("0", "1"), each = 5),
a = rep(1:5,2),
b = c(7,8,9,10,11,6,8,9,10,12),
x = c(1:5, 1:5),
y = c(1:3,5,6,1.1,2.1,4.1,5.1,7.1),
stringsAsFactors=F)
In order to assign 2 in unclass() to 0 in split, I did the following.
foo <- arrange(foo, desc(split))
foo$split <- as.factor(foo$split)
#> str(foo)
#'data.frame': 10 obs. of 5 variables:
# $ split: Factor w/ 2 levels "0","1": 2 2 2 2 2 1 1 1 1 1
# $ a : int 1 2 3 4 5 1 2 3 4 5
# $ b : num 6 8 9 10 12 7 8 9 10 11
# $ x : int 1 2 3 4 5 1 2 3 4 5
# $ y : num 1.1 2.1 4.1 5.1 7.1 1 2 3 5 6
Once again, 0 has 2 in unclass().
#> unclass(foo$split)
# [1] 2 2 2 2 2 1 1 1 1 1
#attr(,"levels")
#[1] "0" "1"
Now I run the following. q (for points) has the ideal outcome. But q2 (for lines) does not.
q <- ggplot(data = foo, aes(x = x, y = y, colour = split))+
geom_point(size = 6)
q2 <- ggplot(data = foo, aes(x = a, y = b, colour = split))+
geom_line()
So, I reversed the factor order and see what happens.
### Reorder the factor levels.
foo$split <- ordered(foo$split, rev(levels(foo$split)))
#> str(foo)
#'data.frame': 10 obs. of 5 variables:
#$ split: Ord.factor w/ 2 levels "1"<"0": 1 1 1 1 1 2 2 2 2 2
#$ a : int 1 2 3 4 5 1 2 3 4 5
#$ b : num 6 8 9 10 12 7 8 9 10 11
#$ x : int 1 2 3 4 5 1 2 3 4 5
#$ y : num 1.1 2.1 4.1 5.1 7.1 1 2 3 5 6
#> unclass(foo$split)
#[1] 1 1 1 1 1 2 2 2 2 2
#attr(,"levels")
#[1] "1" "0"
Both q3 and q4 got the correct outcomes.
q3 <- ggplot(data = foo, aes(x = x, y = y, colour = split))+
geom_point(size = 6)
q4 <- ggplot(data = foo, aes(x = a, y = b, colour = split))+
geom_line()
So, Here is the final form.
ggplot(data = foo)+
geom_point(aes(x = x, y = y, colour = split), size = 6)+
geom_line(aes(x = a, y = b, colour = split))