Color one point and add an annotation in ggplot2?

Question

I have a dataframe a with three columns :

GeneName, Index1, Index2

I draw a scatterplot like this

Answer 1

Something like this should work. You may need to mess around with the x and y arguments to geom_text().

library(ggplot2)

highlight.gene <- "G1"

set.seed(23456)
a <- data.frame(GeneName = paste("G", 1:10, sep = ""),
                   Index1 = runif(10, 100, 200),
                   Index2 = runif(10, 100, 150))

a$highlight <- ifelse(a$GeneName == highlight.gene, "highlight", "normal")
textdf <- a[a$GeneName == highlight.gene, ]
mycolours <- c("highlight" = "red", "normal" = "grey50")

a
textdf

ggplot(data = a, aes(x = Index1, y = Index2)) +
    geom_point(size = 3, aes(colour = highlight)) +
    scale_color_manual("Status", values = mycolours) +
    geom_text(data = textdf, aes(x = Index1 * 1.05, y = Index2, label = "my label")) +
    theme(legend.position = "none") +
    theme()