R help - Apr 2014 - Manipulating x axis using scale_x_continuous (but a factor is used). Is there a work around?

My code that I've used is:

    mcgc <- ggplot(sam, aes(x = person,y = m, colour = X)) +
                  geom_point(size = 0.75) +
                  scale_colour_gradient2(high="red",
mid="green",
limits=c(0,1), guide = "colourbar") +
                  geom_hline(aes(yintercept = mad, linetype = "mad"),
colour = "blue", size=0.75, show_guide = TRUE) +
                  geom_hline(aes(yintercept = mmad, linetype "mmad"),
colour = "black", size=0.75, show_guide = TRUE)  +
                  facet_wrap(~ Plan, scales = "free", ncol = 4) +
                  scale_linetype_manual(name = "Plan of Health Care",
values = c("mad" = 1, "mmad" = 1),guide =
"legend")

For this data:

Data:

    Plan  Person X       m  mad  mmad
    1  1 95 0.323000 0.400303 0.12
    1  2 275 0.341818 0.400303 0.12
    1  3  2 0.618000 0.400303 0.12
    1  4 75 0.320000 0.400303 0.12
    1  5 13 0.399000 0.400303 0.12
    1  6 20 0.400000 0.400303 0.12
    2  7 219 0.393000 0.353350 0.45
    2  8 50 0.060000 0.353350 0.45
    2  9 213 0.390000 0.353350 0.45
    2  15 204 0.496100 0.353350 0.45
    2  19 19 0.393000 0.353350 0.45
    2  24 201 0.388000 0.353350 0.45
    3  30 219 0.567 0.1254 0.89
    3  14 50 0.679 0.1254 0.89
    3  55 213 0.1234 0.1254 0.89
    3  18 204 0.6135 0.1254 0.89
    3  59 19 0.39356 0.1254 0.89
    3  101 201 0.300 0.1254 0.89

I'm trying to manipulate the x axis using the following, only because
the data can get very large and there is just way too many Persons to
fit on the x-axis and I need to reduce it so its legible:

    scale_x_continuous(breaks = c(min(person), median(person),
max(person)), labels = c(min(person), median(person), max(person)))

However, given that I had to change `person` into a factor to order
the data properly, the above code does not work.  I get the errors,
depending on how I fiddle around with the code:

    Error: Discrete value supplied to continuous scale
    Error in Summary.factor(c(1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 11L,  :
      min not meaningful for factors

Changing `person` to numeric does not work, as the accumulated
`person` for the entire dataset will then be on each Plan figure
panel, as opposed to the scale specific for each Plan. That is, the
x-axis for each panel (Plan) should have a scale beginning from its
lowest Person to its highest Person (ie Plan 1 should have an x-axis
that goes from 1 to 6 but Plan 3 has one that goes from 14 to 101).
Changing the Person to numeric, the x-axis for all panels starts at 1
and goes to 101.

Is there a work around for this?