[R] Changing colour of continuous time-series in ggplot2

[joeP]

Hi, 

This seems like there should be a simple answer, but having spent most of
the day trying to find it, I'm becoming less convinced and as such am asking
it here. 

Here's a sub-set of my data (a data.frame in R): 

myDF 
                                time     value      trial 
1   2011-03-01 01:00:00  64092  FALSE 
2   2011-03-01 02:00:00  47863  FALSE 
3   2011-03-01 03:00:00  43685  FALSE 
4   2011-03-01 04:00:00  44821   TRUE 
5   2011-03-01 05:00:00  48610   TRUE 
6   2011-03-01 06:00:00  44856   TRUE 
7   2011-03-01 07:00:00  55199   TRUE 
8   2011-03-01 08:00:00  69326  FALSE 
9   2011-03-01 09:00:00  84048  FALSE 
10 2011-03-01 10:00:00  81341  FALSE 

>From this, I can plot a simple time-series in ggplot: 

ggplot(myDF, aes(time,value)) + geom_line() 

but I'd like to change the colour of the line based on whether the trial
value is TRUE or FALSE, so I try: 

ggplot(myDF, aes(time,value)) + geom_line(aes(colour=trial)) 

but this draws a line from the value on row 3 to that on row 8 (essentially
plotting TRUE and FALSE as separate data-sets).  I've tried using various
other geometries (inc. geom_path()) but all have produced similar events. 
Is there a way I can plot the time-series in a continuous way (i.e. as one
data-set) and change only the colour of the line? 

Thanks, 
Joe


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