R help - Sep 2012 - Lattice bwplot(): Conditioning on one factor

I'm not able to create the proper syntax to specify a lattice bwplot() for
only one of two conditioning factors.

   The syntax that produces a box plot of each of the two conditioning
factors is:

bwplot(quant ~ param | era, data=mg.d, main='Dissolved Magnesium',
ylab='Concentration (mg/L)')

   What I've tried unsuccessfully are:

bwplot(quant ~ param | factor(era=='Pre-mining'), data=mg.d,
main='Magnesium', ylab='Concentration (mg/L))

bwplot(quant ~ param | era, data=mg.d, main='Magnesium',
ylab='Concentration
(mg/L)', subset=era('Pre-mining'))

plus slight variations of the above. None work.

   Please point me to what I've missed in specifying only one of two
conditioning factors for the plot.

Rich

On Sep 28, 2012, at 7:49 AM, Rich Shepard wrote:
>  I'm not able to create the proper syntax to specify a lattice bwplot()
for
> only one of two conditioning factors.
Wouldn't that involve specifying the 'subset' parameter (if bwplot
accepts a subset argument) or using the 'subset' function to pass the
desired rows to the data argument if it doesn't?
> 
>  The syntax that produces a box plot of each of the two conditioning
> factors is:
> 
> bwplot(quant ~ param | era, data=mg.d, main='Dissolved Magnesium',
ylab='Concentration (mg/L)')
> 
>  What I've tried unsuccessfully are:
> 
> bwplot(quant ~ param | factor(era=='Pre-mining'), data=mg.d,
> main='Magnesium', ylab='Concentration (mg/L))
> 
> bwplot(quant ~ param | era, data=mg.d, main='Magnesium',
ylab='Concentration
> (mg/L)', subset=era('Pre-mining'))
> 
> plus slight variations of the above. None work.
> 
>  Please point me to what I've missed in specifying only one of two
> conditioning factors for the plot.
> 
> 
-- 

David Winsemius, MD
Alameda, CA, USA