Use position_jitterdodge without mapping aesthetic - r

Question

I would like to produce a plot like the one obtained with the code below. However, I would like to dodge by "replicate", but without actually mapping an aesthetic (because I would like to assign fill and colors to other aesthetics).
dataset <- data_frame(sample = rep(c("Sample1","Sample2","Sample3", "Sample4"), each = 25),
replicate = sample(x = c("A", "B"), size = 100, replace = TRUE),
value = rnorm(n = 100, mean = 0, sd = 10))
ggplot(data = dataset, aes(x = sample, y = value, fill = replicate)) +
geom_point(position = position_jitterdodge(jitter.width = 0.15, dodge.width = 0.75),
show.legend = F)
I had hope using group = replicate instead of fill = replicate but this doesn't work. I can imagine a workaround using for example alpha = replicate as an aesthetic and setting scale_alpha_manual(values = c(1, 1)) in case of duplicates, but I don't find this solution ideal and would like to keep all aesthetics available (other than x and y available for further use)
ggplot(data = dataset, aes(x = sample, y = value, alpha = replicate)) +
geom_point(position = position_jitterdodge(jitter.width = 0.15, dodge.width = 0.75),
show.legend = F) +
scale_alpha_manual(values = c(1, 1))
The plot that I expect to get is:
I hope my question makes sense, any hint ?
Best,
Yvan

Answer 1

You could unite the sample and replicate columns and use that as the x-axis, injecting a 'Placeholder' value for spacing between samples.
library(tidyverse)
set.seed(20181101)
dataset <- data_frame(sample = rep(c("Sample1","Sample2","Sample3", "Sample4"), each = 25),
replicate = sample(x = c("A", "B"), size = 100, replace = TRUE),
value = rnorm(n = 100, mean = 0, sd = 10))
dataset %>%
bind_rows({
#create a dummy placeholder to allow for spacing between samples
data.frame(sample = unique(dataset$sample),
replicate = rep("Placeholder", length(unique(dataset$sample))),
stringsAsFactors = FALSE)
}) %>%
#unite the sample & replicate columns, and use it as the new x-axis
unite(sample_replicate, sample, replicate, remove = FALSE) %>%
ggplot(aes(x = sample_replicate, y = value, color = replicate)) +
geom_jitter() +
#only have x-axis labels for each sample
scale_x_discrete(breaks = paste0("Sample", 1:length(unique(dataset$sample)), "_B"),
labels = paste0("Sample ", 1:length(unique(dataset$sample)))) +
labs(x = "Sample") +
#don't show the Placeholder value in the legend
scale_color_discrete(breaks = c("A", "B"))