I think you are looking for this:
require(ggplot2)
df <- data.frame(x=seq(1, 1e9, length.out=100), y=sample(100))
# displays x-axis in scientific notation
p <- ggplot(data = df, aes(x=x, y=y)) + geom_line() + geom_point()
p
# displays as you require
require(scales)
p + scale_x_continuous(labels = comma)
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