R help - Jan 2012 - Lattice: Understanding How Points Connected by Lines

A data frame has one factor, one date, and one numeric column. When I plot
these using the default pch of the open circle (first attachment),

xyplot(TDS ~ sampdate | she.s, data = sheep.cast, main = 'TDS in Sheep
Creek', ylab = 'Concentration (mg/L)', xlab = 'Time')

I see the higher concentration points toward the right on several panels.
But, when I change to using a line type (second attachment),

xyplot(TDS ~ sampdate | she.s, data = sheep.cast, type = 'l', main =
'TDS in
Sheep Creek', ylab = 'Concentration (mg/L)', xlab = 'Time')

the higher concentrations are connected to points far to the left (earlier
years). I expected to see a line with a few spikes toward the right sides of
the panels.

   Where do I start to look for the reason for this behavior?

TIA,

Rich
-------------- next part --------------
A non-text attachment was scrubbed...
Name: sheep-TDS-year-dot.pdf
Type: application/pdf
Size: 6593 bytes
Desc: 
URL:
<https://stat.ethz.ch/pipermail/r-help/attachments/20120101/1ff6eec5/attachment.pdf>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: sheep-TDS-year-line.pdf
Type: application/pdf
Size: 6317 bytes
Desc: 
URL:
<https://stat.ethz.ch/pipermail/r-help/attachments/20120101/1ff6eec5/attachment-0001.pdf>

On Sun, 1 Jan 2012, Rich Shepard wrote:
>  Where do I start to look for the reason for this behavior?
   Perhaps the dates are not in sequence? So I need to use zoo to order the
dates sequentially?

Rich

On Jan 1, 2012, at 5:50 PM, Rich Shepard wrote:
>  A data frame has one factor, one date, and one numeric column. When  
> I plot
> these using the default pch of the open circle (first attachment),
>
> xyplot(TDS ~ sampdate | she.s, data = sheep.cast, main = 'TDS in Sheep
> Creek', ylab = 'Concentration (mg/L)', xlab = 'Time')
>
> I see the higher concentration points toward the right on several  
> panels.
> But, when I change to using a line type (second attachment),
>
> xyplot(TDS ~ sampdate | she.s, data = sheep.cast, type = 'l', main
=
> 'TDS in
> Sheep Creek', ylab = 'Concentration (mg/L)', xlab =
'Time')
>
> the higher concentrations are connected to points far to the left  
> (earlier
> years). I expected to see a line with a few spikes toward the right  
> sides of
> the panels.
>
>  Where do I start to look for the reason for this behavior?
You should look at the structure of your dataset variables and the  
order in which they occur  ... none  of which is "visible" in what you
have offered.

-- 

David Winsemius, MD
West Hartford, CT