R: ggplot annotate geom_text with position_dodge and facets - r

Question

I have an R dataframe data (made with dplyr) that I'm trying to plot with ggplot():
require(dplyr)
data <- structure(list(gGroup = structure(c(1L, 1L, 1L, 1L, 2L, 2L, 2L,
2L, 3L, 3L, 3L, 3L), .Label = c("MC", "R", "UC"), class = "factor"),
Episode = structure(c(2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L,
2L, 2L, 2L), .Label = c("Morning", "Day", "Night", "24 hour"
), class = "factor"), variable = c("HF", "HF", "LF", "LF",
"HF", "HF", "LF", "LF", "HF", "HF", "LF", "LF"), parameter = c("RR",
"RT", "RR", "RT", "RR", "RT", "RR", "RT", "RR", "RT", "RR",
"RT"), mean = c(3.90575222833804, 4.24572828952087, 5.14491629837998,
3.88189313775535, 4.02908403079823, 3.91129824615597, 4.73913642980089,
3.63973850905423, 4.66445796048274, 4.21723744674943, 5.57765585365275,
4.01444148455851), sd = c(1.09129154084895, 1.43102672123806,
1.17782114274004, 1.33381488706382, 1.33497319178289, 1.22259231099975,
1.33329948427898, 1.09625319168102, 1.19876558625356, 1.73746797295816,
1.05862249404741, 1.91144835753868), se = c(0.199241664579179,
0.261268538538247, 0.215039736195078, 0.243520167060353,
0.471984298305965, 0.432251656867227, 0.471392553343098,
0.387584032867524, 0.215304655178374, 0.312058460044998,
0.190134212775724, 0.343306259564318)), .Names = c("gGroup",
"Episode", "variable", "parameter", "mean", "sd", "se"), class = c("grouped_df",
"tbl_df", "tbl", "data.frame"), row.names = c(NA, -12L), drop = TRUE, indices = list(
0:1, 2:3, 4:5, 6:7, 8:9, 10:11), group_sizes = c(2L, 2L,
2L, 2L, 2L, 2L), biggest_group_size = 2L, labels = structure(list(
gGroup = structure(c(1L, 1L, 2L, 2L, 3L, 3L), .Label = c("MC",
"R", "UC"), class = "factor"), Episode = structure(c(2L,
2L, 2L, 2L, 2L, 2L), .Label = c("Morning", "Day", "Night",
"24 hour"), class = "factor"), variable = c("HF", "LF", "HF",
"LF", "HF", "LF")), .Names = c("gGroup", "Episode", "variable"
), class = "data.frame", row.names = c(NA, -6L)))
Currently I'm using the following code to plot:
require(ggplot2)
require(ggthemes)
pd <- position_dodge(width=0.9)
p <- ggplot(data, aes(x = gGroup, y = mean, fill = variable)) +
facet_grid(parameter~Episode) +
geom_bar(stat="identity", position=pd) +
geom_errorbar(aes(ymin = mean-se, ymax = mean+se), width = .3, position=pd) +
theme_hc() + scale_fill_hc() +
labs(y = "Logit transform of spectral power (m/s2), mean±SE", x= NULL)
ann_text <- data.frame(gGroup = "MC", mean = 6, variable = "LF", parameter = "RR", Episode = "Day")
p + geom_text(aes(ymax = 6.5, width = .2), data = ann_text, label="*", position=pd)
This gives me the following plot:
I'm quite satisfied with the result, but as you can see the asterisk isn't aligned correctly. I looked it up online, and I read this and this and the manual.
Everyone I see the suggestions to use position=position_dodge(width=0.9), but this doesn't help for me. I tried hjust to maybe move the asterisk to the right position, but that's of no use either. Funny thing is that my error bars are aligned correctly.
I feel like I'm overlooking something very simple, but I cannot figure out what it is.
I'm using R 3.1.3 on OSX 10.10.2, and loading the newest versions of ggplot2 and ggthemes.

Answer 1

In order for position_dodge to work, there needs to be a reason to dodge. That is you need to change the ann_text appropriately with variable = c("LF", "HF"), so that there is a reason to dodge. Then just define the label appropriately. Below I assume you just want the * over the LF bar.
ann_text <- data.frame(gGroup = rep("MC",2),
mean = 6,
variable = c("LF", 'HF'),
label = c("*", ""),
parameter = "RR",
Episode = "Day")
p + geom_text(aes(ymax = 6.5, width = .2, label = label), data = ann_text, position=pd)