Condional Density Plot from different data

Perhaps I found a solution as:

datA$type <- gl(1, nrow(datA), label = 'PopA')
datB$type <- gl(1, nrow(datB), label = 'PopB')
dat <- rbind(datA, datB)

Or, slightly shorter

dat <- make.groups(datA, datB)
densityplot(~scores|condition, groups = which, dat)

[...]

library(lattice)
densityplot(~datA$scores + datB$scores|datA$condition)

The problem here is that datA$scores and datB$scores don't have the
same length. This requirement is implicit in the description of the
extended formula interface:

          'y1 + y2 ~ x | a * b' [...] would be taken to mean that the
user wants to plot
          both 'y1 ~ x | a * b' and 'y2 ~ x | a * b' [...] superposed
in each panel.

and the latter formulae would make sense only if x, a, b, and y1 (and
y2) have the same length.

-Deepayan