Add text to plot with facetted bar chart

Question

My question is related to this question. I want "2014" in the 4-year facet. I tried to repeat but my code doesn't give what I want.

Annotating text on individual facet in ggplot2

This is my data

structure(list(Rot = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 
3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L), .Label = c("2-year", 
"3-year", "4-year"), class = "factor"), Rot.Herb = structure(c(3L, 
3L, 4L, 4L, 13L, 13L, 14L, 14L, 5L, 5L, 6L, 6L, 9L, 9L, 10L, 
10L, 15L, 15L, 16L, 16L, 1L, 1L, 2L, 2L, 7L, 7L, 8L, 8L, 11L, 
11L, 12L, 12L, 17L, 17L, 18L, 18L), .Label = c("A4-conv", "A4-low", 
"C2-conv", "C2-low", "C3-conv", "C3-low", "C4-conv", "C4-low", 
"O3-conv", "O3-low", "O4-conv", "O4-low", "S2-conv", "S2-low", 
"S3-conv", "S3-low", "S4-conv", "S4-low"), class = "factor"), 
    variable = structure(c(1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 
    2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 
    1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L), .Label = c("Diversity", 
    "Evenness"), class = "factor"), N = c(4, 4, 4, 4, 4, 4, 4, 
    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 
    4, 4, 4, 4, 4, 4, 4, 4, 4, 4), value = c(0.78537789925, 0.613408315, 
    1.305194686, 0.79519430975, 0.4481728555, 0.30608817425, 
    1.20978861475, 0.8580643725, 0.92387324875, 0.630166121, 
    0.945954185, 0.561172324, 1.43952456275, 0.8616864655, 1.23679146725, 
    0.831737624, 1.033474108, 0.80689293925, 0.9910142125, 0.79342098075, 
    1.175512223, 0.6293940245, 0.981614832, 0.62342189825, 1.351710013, 
    0.805075937, 1.6598348325, 0.7983622545, 1.01606920875, 0.5751418795, 
    1.0500365255, 0.56408326225, 1.07162937725, 0.6756859865, 
    0.45699816625, 0.44444147325), sd = c(0.354077266902404, 
    0.208934910331856, 0.169501822767995, 0.0774319459391732, 
    0.737366460962239, 0.40697977697835, 0.494107033311986, 0.11906912863268, 
    0.491492768082854, 0.34236657107712, 0.219739438843007, 0.205905593411204, 
    0.319301583035043, 0.0696484379979274, 0.0563293598951725, 
    0.0978700910274188, 0.446850757364563, 0.175073468716825, 
    0.426859848850874, 0.180469101499932, 0.526842123835502, 
    0.200470277385505, 0.574885944755375, 0.27189545397305, 0.39621771945215, 
    0.150798258847229, 0.275863362594154, 0.111178397407429, 
    0.254811233135664, 0.158920851982914, 0.198698241334475, 
    0.0730606635175717, 0.717706309307313, 0.453776579066358, 
    0.574276936403411, 0.513758415496589), se = c(0.177038633451202, 
    0.104467455165928, 0.0847509113839974, 0.0387159729695866, 
    0.368683230481119, 0.203489888489175, 0.247053516655993, 
    0.0595345643163399, 0.245746384041427, 0.17118328553856, 
    0.109869719421504, 0.102952796705602, 0.159650791517521, 
    0.0348242189989637, 0.0281646799475863, 0.0489350455137094, 
    0.223425378682282, 0.0875367343584126, 0.213429924425437, 
    0.090234550749966, 0.263421061917751, 0.100235138692753, 
    0.287442972377688, 0.135947726986525, 0.198108859726075, 
    0.0753991294236146, 0.137931681297077, 0.0555891987037145, 
    0.127405616567832, 0.0794604259914568, 0.0993491206672376, 
    0.0365303317587859, 0.358853154653656, 0.226888289533179, 
    0.287138468201705, 0.256879207748294), ci = c(0.563415944919255, 
    0.332462066715199, 0.26971522480343, 0.123211505132525, 1.1733145846647, 
    0.647595643784969, 0.786234551289211, 0.189465554245211, 
    0.782074671929471, 0.544781614588516, 0.349654482635521, 
    0.327641747494367, 0.508080071600555, 0.110826207087643, 
    0.089632581638694, 0.155733154793995, 0.71103927089404, 0.278580956835532, 
    0.679229274424713, 0.287166612643164, 0.838323385234058, 
    0.318992946792351, 0.914771825423139, 0.432646341459985, 
    0.630470808679215, 0.23995368085579, 0.438960169525453, 0.176909640028318, 
    0.40546153371869, 0.252878539112781, 0.316173242000635, 0.116255819336536, 
    1.14203089616693, 0.722059798737006, 0.91380275723334, 0.817504285602766
    )), .Names = c("Rot", "Rot.Herb", "variable", "N", "value", 
"sd", "se", "ci"), row.names = c(NA, -36L), class = "data.frame")

and the code to graph

p <- ggplot(Shannon.long2, aes(x=Rot.Herb, y=value, fill=factor(variable)))+
  geom_bar(stat="identity", position="dodge")+
  scale_fill_brewer(palette = "Set1")+
  theme_bw() +
  theme(panel.grid.major=element_blank()) +
  facet_grid(~Rot, scales = "free_x", space="free_x")+
  theme(legend.title=element_blank(),legend.text=element_text(size=20),legend.position="top")+
  geom_errorbar(aes(ymin=value-se, ymax=value+se), size=0.5, width=.25,position=position_dodge(.9))+
  xlab("\nTreatment") +
  theme(axis.title = element_text(size=24,face="bold", vjust=4), axis.text.x = element_text(size=20,angle = 90, hjust = 1)) +
  ylab("Shannon's H' and E'") +
  theme(axis.title = element_text(size=24,face="bold", vjust=2), axis.text.y = element_text(size=20, color="black"))+
  theme(strip.text.x = element_text(colour = "black", size = 20), strip.background = element_rect(fill = "white"))

produced graph (please don't mind the "2014" on the y-axis).

New code to annotate 2014, with help from eipi10

 ann_text <- data.frame(x = "S4-conv",y = 1.75,lab = "2014", Rot.Herb=NA, 
value=NA, variable=NA, 
N=NA, sd=NA, se=NA, ci=NA, 
Rot = factor("4-year",levels = c("2-year","3-year","4-year")))

I got an error saying Error: Discrete value supplied to continuous scale after I run p + geom_text(data = ann_text,label = "2014"). Please see what have been wrong with my code and data format. Thanks.

Answer 1

It turns out the issue is that when you include value=NA in ann_text it gets interpreted as logical (rather than numeric, which is its mode in Shannon.long2), causing the error because ggplot expects a numeric variable rather than a categorical one. Set value=NA_real_ (in addition to NA, R has class-specific missing value constants; see ?NA for more info) in ann_text to ensure value is interpreted as numeric and resolve the error. Or set value to any number, e.g., value=0.

In the example below, I've removed all of the theme and lab statements to shorten the code down to the essentials:

p = ggplot(Shannon.long2, aes(x=Rot.Herb, y=value, fill=factor(variable))) +
  geom_bar(stat="identity", position="dodge") +
  geom_errorbar(aes(ymin=value-se, ymax=value+se), size=0.5, width=.25,position=position_dodge(.9)) +
  facet_grid(~Rot, scales = "free_x", space="free_x")

ann_text <- data.frame(x = "S4-conv", y = 1.75, lab = "2014", Rot.Herb=NA, 
                       value=NA_real_, variable=NA)

p + geom_text(data = ann_text, aes(label=lab, x, y))

Note that you also need to feed x and y values to geom_text to provide the label location.

Another option would be to just use the same x and y variable names as in your original data frame, since ggplot already knows these names and has scaled the graph based on them. Now the only missing column we need to add is variable:

ann_text <- data.frame(Rot.Herb = "S4-conv", value = 1.75, lab = "2014", variable=NA)

p + geom_text(data = ann_text, aes(label=lab, Rot.Herb, value))