duplicating and edit a discrete axis in ggplot2 - 2021 - r

Question

There are a couple of other posts on the same topic, but the solutions proposed do not fit my case.
Given a data frame like this
ddff <- structure(
list(
SampleID = structure(
20:16,
.Label = c(
"S39",
"S30",
"S35",
"S22",
"S23",
"S26",
"S29",
"S24",
"S27",
"S32",
"S37",
"S36",
"S38",
"S34",
"S33",
"S40",
"S25",
"S28",
"S31",
"S21"
),
class = "factor"
),
Counts = c(12177, 14367, 15118, 15312,
16622),
sampleName = structure(
20:16,
.Label = c(
"2Dr",
"2Es",
"1Er",
"1Bs",
"1Cs",
"2As",
"2Ds",
"1Ds",
"2Bs",
"1Br",
"2Br",
"2Ar",
"2Cr",
"1Dr",
"1Cr",
"2Er",
"1Es",
"2Cs",
"1Ar",
"1As"
),
class = "factor"
),
compartment = c("soil", "root", "soil",
"soil", "root")
),
row.names = c(NA, 5L),
class = "data.frame"
)
and the following code
library(tidyverse)
ddff %>%
ggplot(aes(x = Counts, y = SampleID)) +
geom_point(aes(col = compartment), size = 4, alpha = 0.75) +
geom_text(
aes(label = paste0(" ", Counts)),
size = 3,
hjust = 0,
nudge_x = -0.1,
check_overlap = TRUE,
color = "blue"
) +
xlim(NA, 33000) +
theme_light() +
theme(plot.title = element_text(hjust = 0.5), aspect.ratio = 1) +
theme(# remove the vertical grid lines
panel.grid.major.x = element_blank(),
panel.grid.minor.x = element_blank()) +
labs(title = "Library Size Overview",
x = "Read Counts",
color = "Compartment") +
theme(
legend.position = c(.95, .95),
legend.justification = c("right", "top"),
legend.box.just = "right",
legend.box.background = element_rect(color = "black", size = 1)
)
I get this plot
Rplot
I'm interested in adding second labels on the right Y axis, according to the content of the ddff column 'sampleName'. Of course the solution seems to be the usage of scale_y_discrete along with dup_axis, but I'm not able to figure out how...any idea based on recent ggplot evolutions?

Answer 1

Discrete scales in ggplot2 don't support secondary scales (see related issue). The ggh4x package has a manual axis that can work around this limitation. (Disclaimer: I'm the author of ggh4x).
For you example, you could use it like this:
library(ggplot2)
# ddff <- structure(...) # omitted for brevity
ggplot(ddff, aes(x = Counts, y = SampleID)) +
geom_point(aes(col = compartment), size = 4, alpha = 0.75) +
geom_text(
aes(label = paste0(" ", Counts)),
size = 3,
hjust = 0,
nudge_x = -0.1,
check_overlap = TRUE,
color = "blue"
) +
xlim(NA, 33000) +
guides(y.sec = ggh4x::guide_axis_manual(
breaks = ddff$SampleID, labels = ddff$sampleName
))
However, you may need to deduplicate data in the axis if there are multiple observations per y-axis category (which isn't the case in the example).

Answer 2

This is a dupe of the ..., and adapting its solution to this is merely adding the scale_y_continuous and setting the y axis label. Unlike teunbrand's excellent answer (I'm a fan of teunbrand's packages/work), this is base ggplot2.
(This also alters the order, since we're now "counting" along the samples.)
ddff %>%
ggplot(aes(x = Counts, y = seq_along(SampleID))) +
geom_point(aes(col = compartment), size = 4, alpha = 0.75) +
geom_text(
aes(label = paste0(" ", Counts)),
size = 3,
hjust = 0,
nudge_x = -0.1,
check_overlap = TRUE,
color = "blue"
) +
xlim(NA, 33000) +
theme_light() +
theme(plot.title = element_text(hjust = 0.5), aspect.ratio = 1) +
theme(# remove the vertical grid lines
panel.grid.major.x = element_blank(),
panel.grid.minor.x = element_blank()) +
labs(title = "Library Size Overview",
x = "Read Counts",
y = "SampleID", # <-- new
color = "Compartment") +
theme(
legend.position = c(.95, .95),
legend.justification = c("right", "top"),
legend.box.just = "right",
legend.box.background = element_rect(color = "black", size = 1)
) +
# new
scale_y_continuous(
breaks = seq_len(nrow(ddff)), labels = ddff$SampleID,
sec.axis = sec_axis(~., breaks = seq_len(nrow(ddff)),
labels = ddff$sampleName)
)