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There are already several questions about this topic (e.g. this one. I also found example code:

# another example; 1d
dat <- data.frame(x=rnorm(20), y=rnorm(20), z=rep(c("a", "b"), each=10))
vline.dat <- data.frame(z=levels(dat$z), vl=c(0,1))
q <- ggplot(dat, aes(x=x, y=y)) +
geom_point() +
geom_vline(aes(xintercept=vl), data=vline.dat) +
facet_grid(z~.)

The code yields this figure: Resulting figure of above code

I have, however not figured out what the difference to my data is and why it is now working. I have the following data frame:

"yaw" "stimulus"
27.927177 30
27.4999279999999 30
-0.5536 90
56.97471 90
65.0127040816326 90
62.33216 90
74.87201 90
67.5808163265306 90
-2.948312 90
68.52282 90
54.9006326530612 90
60.4753 90
64.53204 90
3.2848 45
26.87405 45
50.8667040816327 45
59.62888 45
53.9892244897959 45
61.27226 45
71.79869 45
88.7793775510204 45
77.78727 45
79.73406 45
104.542 45
114.92185 45
140.76407 45
131.187357142857 45
169.08197 45
-137.36238 45
-147.789030612245 45
5.7612 60
8.7396 60
-1.06195918367347 60
4.52126 60
10.05313 60
10.8253469387755 60
9.49371 60
29.9075 60
28.0361530612245 60
-9.32023 60
-57.9522755102041 60
-61.5898 60
-66.23353 60
-53.1884387755102 60
-40.41378 60
-16.734 60
-5.66388 60
3.58145 60

My data frame for the bars looks like this:

stimuli <- data.frame(groups = c(90, 60, 45, 30),
         pos = c(-90, 60, 45, 30))

And my plotting code looks like this:

fig <- ggplot(df, aes(yaw, group = stimulus)) +
geom_histogram(binwidth = 1, aes(y = 0.5 * ..density..)) +
   scale_x_continuous(breaks = c(-180, -90, 0, 90, 180)) +
   ylab("Count") + xlab("Yaw Angle [º]") +
facet_grid(stimulus ~ .) +
# add vertical lines at the bar positions
geom_vline(data = stimuli, aes(xintercept = pos, colour = "red"))

My figure Each facet should only contain one of the red vertical bars. Can you point me to the error?

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mrub
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  • Thank you for your comment, Roland. For me, adding the group aesthetic does not work, however. Did you get the result with only one bar per facet? – mrub Aug 25 '14 at 14:17

1 Answers1

2

Just rename the column in stimuli (so facet_grid recognizes it as the facetting variable):

names(stimuli)[1] <- "stimulus"


library(ggplot2)
fig <- ggplot(DF, aes(yaw)) +
  geom_histogram(binwidth = 1, aes(y = 0.5 * ..density..)) +
  scale_x_continuous(breaks = c(-180, -90, 0, 90, 180)) +
  ylab("Count") + xlab("Yaw Angle [º]") +
  facet_grid(stimulus ~ .) +
  # add vertical lines at the bar positions
  geom_vline(data = stimuli, aes(xintercept = pos), colour = "red")

print(fig)

resulting plot

Roland
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