Add character variable (weekdays) to plot - r

Question

I want to add on this plot the weekday as text on top of the bars.
The only function to add text in ggplot I found, is "annotate", which does not work the way I want.
It should look like this:
Plot with weekdays
geom_text gives me this
Geom_text
My code:
ggplot(data = filter(T2G2_dayav, site %in% c("S17S", "S17N"), !is.na(distance)),
mapping = aes(as.factor(x = date_days))) +
geom_col(mapping = aes(y = T2pn_av, fill = as.factor(distance)),
position = position_dodge(width = 0.9)) +
theme_bw() + ylab("Particle Number (#/cm³), day-av") + xlab("Date") +
scale_y_continuous(limits = c(0, 30000)) +
scale_fill_discrete(name = "T2, Distance from road (m)") +
scale_color_grey(name = "Reference intrument G2") +
ggtitle("Day-averaged Particle Number (PN) per distance")
the head of my data:
distance date_days site T2pn_av T2pn_avambient T2wdir_med weekday Date G2pn_av G2pn_min G2pn_max G2ws_av G2ws_min G2ws_max G2wdir_med
<int> <dttm> <chr> <dbl> <dbl> <dbl> <chr> <dttm> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
1 -10 2017-07-18 S17N 28814.83 16917.831 110 Di 2017-07-18 13655.29 4621 105100 0.6781284 0 3.6 51.0
2 -10 2017-07-19 S17N 24210.95 15565.951 100 Mi 2017-07-19 10627.73 2908 67250 1.3673618 0 5.5 70.0
3 -10 2017-07-24 S17N 16143.44 7907.442 80 Mo 2017-07-24 11686.54 3582 55080 0.8178753 0 4.8 95.5
4 -10 2017-07-29 S17N 11762.56 5574.563 270 Sa 2017-07-29 12180.73 5413 45490 1.0304985 0 5.7 265.0
5 -10 2017-07-30 S17N 12138.22 6360.225 290 So 2017-07-30 10404.75 6113 23860 1.2385791 0 6.6 274.0
6 -10 2017-07-31 S17N 13815.32 9008.320 270 Mo 2017-07-31 11849.89 4595 46270 0.8554044 0 4.4 230.0
dput(head(T2G2_dayav))
structure(list(distance = c(-10L, -10L, -10L, -10L, -10L, -10L
), date_days = structure(c(1500328800, 1500415200, 1500847200,
1501279200, 1501365600, 1501452000), class = c("POSIXct", "POSIXt"
), tzone = "Europe/Berlin"), site = c("S17N", "S17N", "S17N",
"S17N", "S17N", "S17N"), T2pn_av = c(28814.8306772908, 24210.9512670565,
16143.442364532, 11762.5630630631, 12138.2247114732, 13815.3198380567
), T2pn_avambient = c(16917.8306772908, 15565.9512670565, 7907.44236453202,
5574.56306306306, 6360.22471147318, 9008.31983805668), T2wdir_med = c(110,
100, 80, 270, 290, 270), weekday = c("Di", "Mi", "Mo", "Sa",
"So", "Mo"), Date = structure(c(1500328800, 1500415200, 1500847200,
1501279200, 1501365600, 1501452000), class = c("POSIXct", "POSIXt"
), tzone = "Europe/Berlin"), G2pn_av = c(13655.2885517401, 10627.7329973352,
11686.5429216867, 12180.7308516181, 10404.7472642001, 11849.8893070109
), G2pn_min = c(4621, 2908, 3582, 5413, 6113, 4595), G2pn_max = c(105100,
67250, 55080, 45490, 23860, 46270), G2ws_av = c(0.678128438241936,
1.36736183524505, 0.817875347544022, 1.0304984658137, 1.23857912107,
0.855404388351763), G2ws_min = c(0, 0, 0, 0, 0, 0), G2ws_max = c(3.6,
5.5, 4.8, 5.7, 6.6, 4.4), G2wdir_med = c(51, 70, 95.5, 265, 274,
230)), .Names = c("distance", "date_days", "site", "T2pn_av",
"T2pn_avambient", "T2wdir_med", "weekday", "Date", "G2pn_av",
"G2pn_min", "G2pn_max", "G2ws_av", "G2ws_min", "G2ws_max", "G2wdir_med"
), row.names = c(NA, -6L), class = c("grouped_df", "tbl_df",
"tbl", "data.frame"), vars = c("distance", "date_days"), drop = TRUE, indices = list(
0L, 1L, 2L, 3L, 4L, 5L), group_sizes = c(1L, 1L, 1L, 1L,
1L, 1L), biggest_group_size = 1L, labels = structure(list(distance = c(-10L,
-10L, -10L, -10L, -10L, -10L), date_days = structure(c(1500328800,
1500415200, 1500847200, 1501279200, 1501365600, 1501452000), class = c("POSIXct",
"POSIXt"), tzone = "Europe/Berlin")), row.names = c(NA, -6L), class = "data.frame", vars = c("distance",
"date_days"), drop = TRUE, .Names = c("distance", "date_days"
)))

Answer 1

The idea is that you add a text on top of every bar (that's why vjust = 0, but you could also do vjust = -.5 to allow more space or vjust = 1.5 to put it in the bars, which is nice as well). The rest within the geom_text ist basically the same as in geom_col. But in general, you could put commonly used aesthetics in the first occurency within ggplot(aes(...)), as you already did with the x-value.
ggplot(data = filter(T2G2_dayav, site %in% c("S17S", "S17N"), !is.na(distance)),
mapping = aes(as.factor(x = date_days))) +
geom_col(mapping = aes(y = T2pn_av, fill = as.factor(distance)),
position = position_dodge(width = 0.9)) +
geom_text(aes(label = weekday, y = T2pn_av), vjust = -.5, # add these
position = position_dodge(width = 0.9)) + # lines
theme_bw() + ylab("Particle Number (#/cm³), day-av") + xlab("Date") +
scale_y_continuous(limits = c(0, 30000)) +
scale_fill_discrete(name = "T2, Distance from road (m)") +
scale_color_grey(name = "Reference intrument G2") +
ggtitle("Day-averaged Particle Number (PN) per distance")
The following should solve your problem with too many labels. It takes the highest label and places it in the center of the bars of that x-value. Find a plot below with additional rows added to your data:
T2G2_dayav <- rbind(T2G2_dayav %>% ungroup(), T2G2_dayav %>% ungroup() %>% mutate(distance = 5)) # add more observations for testing
T2G2_dayav <- T2G2_dayav %>% mutate(T2pn_av = ifelse(distance == 5, T2pn_av/2, T2pn_av)) # label only the highest bar
The following should work with your data:
ggplot(data = filter(T2G2_dayav, site %in% c("S17S", "S17N"), !is.na(distance)) %>%
group_by(date_days) %>% # group by days
mutate(weekday2 = ifelse(T2pn_av == max(T2pn_av), weekday, NA)), # within each day (group), only label the highest
mapping = aes(as.factor(x = date_days))) +
geom_col(mapping = aes(y = T2pn_av, fill = as.factor(distance)),
position = position_dodge(width = 0.9)) +
geom_text(aes(label = weekday2, y = T2pn_av), vjust = -.5, # add these
position = position_dodge(with = 0.9)) + # lines
theme_bw() + ylab("Particle Number (#/cm³), day-av") + xlab("Date") +
scale_y_continuous(limits = c(0, 30000)) +
scale_fill_discrete(name = "T2, Distance from road (m)") +
scale_color_grey(name = "Reference intrument G2") +
ggtitle("Day-averaged Particle Number (PN) per distance")