Preserve tip lengths in dendrogram (similarly to `plot.hclust()`)

[almeidasilvaf]

Hi, @thomasp85

First of all, thank you for this great package!

I've been trying to use {ggraph} to create a dendrogram that preserves tip lengths as plot.hclust() does, but I can't seem to make it work. I was wondering if there is already an easy to do this with geom_edge_elbow().

In the reprex below, I demonstrate that I can do what I want with a hacky way by using data produced by {ggdendro}, but I don't like this approach. Is there a more elegant way of doing the same using {ggraph}?

suppressPackageStartupMessages(library(ggplot2))

# Simulate data
simdata <- matrix(
    rnorm(100 * 50, mean = 10, sd = 2),
    nrow = 100
)
cormat <- cor(t(simdata))
hc <- hclust(as.dist(1 - cormat), method = "average")

# 1) The base R way
plot(hc, labels = FALSE)

# 2) The {ggraph} way
p1 <- ggraph::ggraph(
    hc, layout = "dendrogram",
    height = .data$height
) +
    ggraph::geom_edge_elbow()

p1

# 3) The {ggdendro} way
p2 <- ggdendro::ggdendrogram(hc, labels = FALSE)
p2

# 4) The hacky way: Extracting x, y, xend, and yend coords with {ggdendro}
ddata <- ggdendro::dendro_data(hc, type = "rectangle")$segments
head(ddata)
#>           x         y      xend      yend
#> 1 39.324219 1.0234122 15.273438 1.0234122
#> 2 15.273438 1.0234122 15.273438 1.0006401
#> 3 15.273438 1.0006401  6.015625 1.0006401
#> 4  6.015625 1.0006401  6.015625 0.9593656
#> 5  6.015625 0.9593656  3.125000 0.9593656
#> 6  3.125000 0.9593656  3.125000 0.8316230

ddata$yend[ddata$yend < 0.05] <- ddata$y[ddata$yend < 0.05] - 0.05

p3 <- ggplot(ddata) +
    geom_segment(
        aes(x = .data$x, y = .data$y, xend = .data$xend, yend = .data$yend), 
        linewidth = 0.3
    ) +
    coord_cartesian(ylim = c(0, NA))

p3

^{Created on 2024-03-25 with reprex v2.1.0}

Best, Fabricio