R Heatmap: conditionally change label text colours with (ggplot2 or plotly) - r

Question

I am trying to produce a heatmap with ggplot2 or plotly in R, where the values associated with a block or tile are used as labels in the respective tile. This was not so difficult, but I have removed the legend and would like to change the colours of the labels conditional on their values to increase their visibility.
Here a reproducible examples to show what I mean.
Data (using data.table and dplyr):
sig <- rep(c("sig1", "sig2", "sig3"), 100, replace = TRUE, prob = c(0.4, 0.35, 0.25))
date <- c("2019-11-01", "2019-11-02", "2019-11-03")
another <- as.data.table(expand.grid(sig, date))
test_dat_numerics <- another[, number_ok := sample(0:100, 900, replace = TRUE)]
setnames(test_dat_numerics, c("Var1", "Var2"), c("sig", "date"))
test_dat_numerics <- test_dat_numerics[, avg := mean(number_ok), by = .(date, sig)] %>%
dplyr::select(-number_ok) %>%
dplyr::rename(number_ok = avg) %>%
dplyr::mutate(prop = ifelse(number_ok > 50, 1, 0))
dplyr::distinct()
The heatmap (with ggplot2):
ggp <- ggplot(test_dat_numerics, aes(date, sig, fill = number_ok)) +
geom_tile() +
geom_text(aes(label = test_dat_numerics$number_ok)) +
theme(legend.position="none")
This results in
The darker a block becomes the less visible the text becomes. To prevent this, my intention is to make the text white when a value is below 50 and black otherwise. This is the part where I failed both with ggplot2 and plotly until now and would be grateful for help.
With plotly:
p <- test_dat_numerics %>%
plot_ly(type = "heatmap",
x = ~date,
y = ~sig,
z = ~number_ok,
# zmax = 100,
# zmin = 0,
showscale = FALSE,
colorscale = "Blues") %>%
add_annotations(text = as.character(test_dat_numerics$number_ok),
showarrow = FALSE,
color = list(if (test_dat_numerics$number_ok[i] > 50) {"black"} else {"white"})) %>%
layout(title = "Test Heatmap",
# titlefont = t,
xaxis = list(title = "Datum"), yaxis = list(title = "Signal")
)
I found a great plotly example here, but I couldn't manage to get to work for my case. Here the annotation part of my code:
ann <- list()
for (i in 1:length(unique(test_dat_numerics$sig))) {
for (j in 1:length(unique(test_dat_numerics$date))) {
for (k in 1:(length(unique(test_dat_numerics$sig))*length(unique(test_dat_numerics$date)))) {
ann[[k]] <- list(
x = i,
y = j,
font = list(color = if (test_dat_numerics$number_ok[i] > 50) {"black"} else {"white"}),
text = as.character(test_dat_numerics$number_ok[[k]]),
xref = "x",
yref = "y",
showarrow = FALSE )
}
}
}
p_test_num_heat <- layout(p, annotations = ann)
Here, one of numerous attempts with ggplot2:
ggp <- ggplot(test_dat_numerics, aes(date, sig, fill = number_ok)) +
geom_tile() +
geom_text(aes(label = test_dat_numerics$number_ok)) +
geom_label(aes(colour = factor(test_dat_numerics$prop))) +
theme(legend.position="none")
(This code produces the plot in the image above if the second to last line is removed.)
I'm pretty stuck on this one... Thanks in advance for any advice!

Answer 1

With ggplot2, you can use colour in the aes of geom_text (+ scale_colour_manual):
ggplot(test_dat_numerics, aes(date, sig, fill = number_ok)) +
geom_tile() +
geom_text(aes(label = number_ok, colour =ifelse(number_ok>50, "black", "white"))) +
scale_colour_manual(values=c("white"="white", "black"="black")) +
theme(legend.position="none")