Adding text in one of the four facets [duplicate] - r

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Annotation on only the first facet of ggplot in R?
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I want to add a few texts in one facet out of four facets in my ggplot.
I am using annotate function to add a text but it generates the text at a given location (x,y) in every facet. Because the data variables have different ranges of y in each facet, the texts are not coming at a desired location (x,y).
Please let me know what should be done. Thanks.
library(dplyr)
library(tidyr)
library(ggplot2)
df%>%
select(Date, Ca, Na, K, Mg)%>%
gather(var,value,-Date)%>%
ggplot(aes(as.Date(Date), value))+
geom_point()+
theme_bw()+
facet_wrap(~var,scales = 'free_y',ncol = 1)+
ylab(" (ppm) (ppm)
(ppm) (ppm)")+
facet_wrap(~var,scales = 'free_y',ncol = 1, strip.position = "right")+
geom_vline(aes(xintercept = as.Date("2021-04-28")), col = "red")+
geom_vline(aes(xintercept = as.Date("2021-04-28")), col = "red")+
geom_vline(aes(xintercept = as.Date("2021-04-29")), col = "red")+
theme(axis.title = element_text(face="bold"))+
theme(axis.text = element_text(face="bold"))+
xlab('Date')+
theme(axis.title.x = element_text(margin = margin(t = 10)))+
theme(axis.title.y = element_text(margin = margin(r = 10)))+
annotate("text", label = "E1", x = as.Date("2021-04-28"), y = 2.8)
This is the code I am using for the desired output. I want to name all the xintercept lines which is E1, E2, E3 (from left to right) on the top of xaxis i.e. above the first facet of variable Ca in the data. Any suggestions?
Here is a part of my data:
df <- read.table(text = "
Date Ca K Mg Na
2/18/2021 1 25 21 19
2/22/2021 2 26 22 20
2/26/2021 3 27 23 21
3/4/2021 4 28 5 22
3/6/2021 5 29 6 8
3/10/2021 6 30 7 9
3/13/2021 7 31 8 10
3/17/2021 8 32 9 11
3/20/2021 9 33 10 12
3/23/2021 10 34 11 13
3/27/2021 11 35 12 14
3/31/2021 12 36 13 15
4/3/2021 13 37 14 16
4/7/2021 14 38 15 17
4/10/2021 15 39 16 18
4/13/2021 16 40 17 19
4/16/2021 17 41 18 20
4/19/2021 8 42 19 21
4/22/2021 9 43 20 22
4/26/2021 0 44 21 23
4/28/2021 1 45 22 24
4/28/2021 2 46 23 25
4/28/2021 3 47 24 26
4/28/2021 5 48 25 27
4/29/2021 6 49 26 28
5/4/2021 7 50 27 29
5/7/2021 8 51 28 30
5/8/2021 9 1 29 31
5/10/2021 1 2 30 32
5/29/2021 3 17 43 45
5/31/2021 6 18 44 46
6/1/2021 4 19 45 47
6/2/2021 8 20 46 48
6/3/2021 2 21 47 49
6/7/2021 3 22 48 50
6/10/2021 5 23 49 51
6/14/2021 3 5 50 1
6/18/2021 1 6 51 2
", header = TRUE)

Answer 1

Prepare the data before plotting, make a separate data for text annotation:
dfplot <- df %>%
select(Date, Ca, Na, K, Mg) %>%
#convert to date class before plotting
mutate(Date = as.Date(Date, "%m/%d/%Y")) %>%
#using pivot instead of gather. gather is superseded.
#gather(var, value, -Date)
pivot_longer(cols = 2:5, names_to = "grp", values_to = "ppm")
dftext <- data.frame(grp = "Ca", # we want text to show up only on "Ca" facet.
ppm = max(dfplot[ dfplot$grp == "Ca", "ppm" ]),
Date = as.Date(c("2021-04-27", "2021-04-28", "2021-04-29")),
label = c("E1", "E2", "E3"))
After cleaning up your code, we can use geom_text with dftext:
ggplot(dfplot, aes(Date, ppm)) +
geom_point() +
facet_wrap(~grp, scales = 'free_y',ncol = 1, strip.position = "right") +
geom_vline(xintercept = dftext$Date, col = "red") +
geom_text(aes(x = Date, y = ppm, label = label), data = dftext, nudge_y = -2)
Try using ggrepel library to avoid label overlap, replace geom_text with one of these:
#geom_text_repel(aes(x = Date, y = ppm, label = label), data = dftext)
#geom_label_repel(aes(x = Date, y = ppm, label = label), data = dftext)
After cleaning up the code and seeing the plot, I think this post is a duplicate of Annotation on only the first facet of ggplot in R? .