lattice/grid: problem with viewports for strips with zero height

PROBLEM
        # Allocating strip labels by the function strip.fun():

    strip.test()
        # Result: No strips: ok. No strings: NOT OK.
        # The distance ``y.text=unit(6,"points")'' is ignored;
        # the strings are not seen on the output.

Looks like a grid bug/feature where non-zero 'y' in grid.text doesn't work 
for viewports with zero height, even if clipping is turned off. Simpler 
example:

grid.text("some text", y = unit(6, "points"), 
          just = c("center", "bottom"), 
          vp = viewport(x = .5, y = .5, h = 0, clip = FALSE))
                                        ^^^^^

(Works if h > 0)

TRIALS FOR WORKAROUNDS

    strip.test( strip.lines=1 )
        # Result: 2 strips: ok, but not whished. 2 strings: ok.

    strip.test( y.text=0 )
        # Result: No strips: ok. 2 strings: ok, but not pretty.

    strip.test( strip.lines=0.01 )
        # Result: 2 very narrow strips: ok, but not whished. 2 strings:
ok.

The third workaround looks OK to me. You can make strip.lines as small as 
you want as long as it's positive.


Anyway, I would take a different approach (creating a new factor) for what 
you are trying to do:




combine.factors <- function(..., sep = "/",
                            drop = FALSE,
                            reverse = FALSE)
{
    ## each argument in ... should be a factor,
    ## first varies fastest

    dots <- lapply(list(...), as.factor)
    dotlevels <- lapply(dots, levels)
    dotchars <- lapply(dots, as.character)
    final.levels <- dotlevels[[1]]
    if (length(dotlevels) > 1)
        for (i in 2:length(dotlevels))
            final.levels <-
                if (reverse)
                    as.vector(t(outer(dotlevels[[i]],
                                      final.levels,
                                      paste, sep = sep)))
                else
                    as.vector(outer(final.levels,
                                    dotlevels[[i]],
                                    paste, sep = sep))
    final.chars <-
        do.call("paste",
                c(if (reverse) rev(dotchars) else dotchars,
                  list(sep = sep)))
    ans <- factor(final.chars, levels = final.levels)
    if (drop) ans <- ans[, drop = TRUE]
    ans
}


data(barley)
dotplot(variety ~ yield | combine.factors(year, site,
                                          sep = "    ",
                                          reverse = TRUE),
        data = barley, layout = c(2, 6))




Deepayan

CODE
    library( lattice )
    library( grid )
    data( barley )

strip.test <- function( strip.lines=0, y.text=unit( 6, "points" ), ...
){ lset( list( clip = list( strip=F ) ) )
    strip.fun <- function( which.given, which.panel, factor.levels, ...
){ grid.text( label=factor.levels[which.panel[which.given]] , x= 0.5 - (
which.given - 1.5 ) * 0.7
            , y=y.text
            , just=c( c("right","left")[which.given], "bottom" )
            )
    }
    print( dotplot( variety ~ yield | year * site, data=barley
        , par.strip.text=list( lines=strip.lines )
        , strip=strip.fun
        , between=list( y=1.5 )
        , ...
        ))
}


Wolfram

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