How do I get discrete factor levels to be treated as continuous?

Question

I have a data frame with columns initially labeled arbitrarily. Later on, I want to change these levels to numerical values. The following script illustrates the problem.

Answer 1

I think you can do this simply by transforming the variable to numeric:

mdf$variable <- as.numeric(as.character(mdf$variable))

g <- ggplot(mdf,aes(variable,value,group=variable,colour=t))
g +
    geom_point() +
    #scale_x_continuous() +
    opts()

Answer 2

You need to convert your factor into numeric:

mdf$numVariable <- as.numeric(as.character(mdf$variable))

g <- ggplot(mdf,aes(numVariable,value,group=variable,colour=t))
g +
    geom_point() +
    #scale_x_continuous() +
    opts()

Or just do the conversion in the call to ggplot:

g <- ggplot(mdf,aes(as.numeric(as.character(variable)),value,group=variable,colour=t))