ggplot geom_line to date axis not working - r

Question

I have several data-sets similar to https://www.dropbox.com/s/j9ihawgfqwxmkgc/pred.csv?dl=0
Loading them from CSV and then plotting works fine
predictions$date <- as.Date(predictions$date)
plot(predictions$date, predictions$pct50)
But when I want to use GGPLOT to draw these data predicted points into a plot to compare them with the original points like:
p = ggplot(theRealPastDataValues,aes(x=date,y=cumsum(amount)))+geom_line()
This command
p + geom_line(predictions, aes(x=as.numeric(date), y=pct50))
generates the following error:
ggplot2 doesn't know how to deal with data of class uneval
But as the first plot(predictions$date, predictions$pct50) works with the data I do not understand what is wrong.
Edit
dput(predictions[1:10, c("date", "pct50")])
structure(list(date = c("2009-07-01", "2009-07-02", "2009-07-03",
"2009-07-04", "2009-07-05", "2009-07-06", "2009-07-07", "2009-07-08",
"2009-07-09", "2009-07-10"), pct50 = c(4276, 4076, 4699.93, 4699.93,
4699.93, 4699.93, 4664.76, 4627.37, 4627.37, 4627.37)), .Names = c("date",
"pct50"), row.names = c(NA, 10L), class = "data.frame")
Edit 2
I change this
p + geom_line(data = predictions, aes(x=as.numeric(date), y=pct50))
and the error changed to:
Invalid input: date_trans works with objects of class Date only
Zusätzlich: Warning message:
In eval(expr, envir, enclos) : NAs created
so I think the hint to How to deal with "data of class uneval" error from ggplot2? (see comments) was a good Idea, bit still the plot does not work.

Answer 1

Your first issue (Edit 2) is because ?geom_line uses mapping=NULL as the first argument, so you need to explicitely state the first argument is data
p + geom_line(data = predictions, aes(x=as.numeric(date), y=pct50))
similar question
Your second issue is because your predictions$date is a character vector, and when using as.numeric it introduces NAs. If you want numerics you need to format it as a date first, then convert it to numeric
as.numeric(as.Date(predictions$date), format="%Y%m%d")