Scatterplot: multiple individual Xs plotted against one Y [duplicate]

Answer 1

Let's say your data is mtcars (built-in) and your one predictor is mpg:

library(ggplot2)
library(reshape2)
mtmelt <- melt(mtcars, id = "mpg")

ggplot(mtmelt, aes(x = value, y = mpg)) +
    facet_wrap(~variable, scales = "free") +
    geom_point()

This is pretty unusual, more commonly you put predictors on the x-axis, but it's what you asked for.