How to add labels to ggplot segment?

Question

I'm trying to add labels to segments I created in a graph using ggplot

dat <- data.frame(start <- c(-1.05113647, -0.63911585, -0.62791554),
                  end <- c(0.37491159, -0.13911585, -0.12791554), 
                  order <- c("Sei whale", "Probeagle", "Northern fur seal"),
                  pos <- c(1, 2, 3)) 

ggplot(dat) + 
  geom_segment(aes(x=start, y=start, xend=end, yend=start), colour = "blue", size = 2) +
  scale_y_reverse() +
  xlab("PC1")+
  ylab(" ")+
  theme_linedraw() + 
  theme(panel.grid.minor = element_blank(), panel.grid.major =   element_blank()) + 
  theme(aspect.ratio = 0.3) +
  theme(legend.position="none") +
  theme(axis.ticks = element_blank(), axis.text.y = element_blank()) 

I'd like to know how to add the names from the "order" to their respective segments.

Answer 1

You can use geom_text() :

library(ggplot2)

ggplot(dat) + 
    geom_segment(aes(start, start, xend = end, yend = start), 
                 colour = "blue",
                 size=4) +
    geom_text(aes((end + start) / 2,
                  y = start, 
                  label = order), 
              color = 'grey75', 
              size = 3, 
              nudge_y = .005) +
    scale_y_reverse() +
    xlab("PC1")+
    ylab(" ")+
    theme_linedraw() + 
    theme(panel.grid.minor = element_blank(), 
          panel.grid.major =   element_blank(),
          aspect.ratio = 0.3,
          legend.position="none",
          axis.ticks = element_blank(), 
          axis.text.y = element_blank()) 

The result is not particularly pretty imo, I increased the segment size , to let the text be visible.

Answer 2

You could try geom_dl() from the directlabels package and expand the x axis a bit:

library(ggplot2)
library(directlabels)

ggplot(dat) + 
  geom_segment(aes(x = start, y = start, xend = end, yend = start), 
               colour = "blue", size = 2) +
  scale_y_reverse() +
  geom_dl(aes(end, start, label = order), 
          method = list(dl.trans(x = x + 0.2), "last.bumpup", cex = 0.60)) +
  scale_x_continuous(expand = c(0, 0.2)) +
  labs(x = "PC1", y = " ") +
  theme_linedraw() + 
  theme(panel.grid.minor = element_blank(), panel.grid.major = element_blank()) + 
  theme(aspect.ratio = 0.7) +
  theme(legend.position = "none") +
  theme(axis.ticks = element_blank(), axis.text.y = element_blank()) 

Which gives:

Note : I changed the aspect.ratio to 0.7 to make it more readable.