[lattice] format and rotation of strip text

https://stat.ethz.ch/pipermail/r-help/2012-November/329479.html

Hopefully [sufficiently] "small, self-contained example":

mailquotes omitted from "start example" to "end example" to
ease rerunning the following code:

# start example
library(reshape2)
library(lattice)

lon=11
lat=7
lev=5
len=lon*lat*lev
array.3d <- array(data=c(1:len), dim=c(lat, lon, lev))

# Rewrite the array values "more spatially," i.e., row-wise from
# bottom left. If there's a more-R-ish way to fill this array as
# desired, please let me know: I know 'for' loops are deprecated
# in R.

i=1
for (z in 1:lev) {
 for (x in lat:1) {
   for (y in 1:lon) {
     array.3d[x,y,z]=i ; i=i+1
   }
 }
}

# produces (with rows=latitudes and cols=longitudes)
array.3d[,,1]
array.3d[,,lev]

# convert data=array.3d to dataframe with reshape2::melt
array.3d.df <- melt(array.3d, varnames=c("lat","lon","lev"),  
value.name="conc")
head(array.3d.df)
tail(array.3d.df)

# make level values {longer, "more realistic"}

array.3d.df$lev <- array.3d.df$lev + 0.12345 # truncated below,  
and ...
# ... below note output from these
head(array.3d.df)
tail(array.3d.df)

# plot "appropriately" for atmospheric data where lev=pressure: use
# * lattice::levelplot
# * one column, since atmospheric levels stack vertically
# * rev(lev), since layers closer to ground level have higher pressure
levelplot(
 conc ~ lon * lat | rev(lev), data=array.3d.df,
 layout=c(1,lev),  # show levels stacked in 1 vertical column
 strip=FALSE,      # this suppresses printing strips atop packets
 strip.left=strip.custom(
   strip.levels=TRUE,  # print level values
   strip.names=FALSE   # don't print name of level variable="rev(lev)"
 )
)
# end example

Note that the (colored) 'strip' for each panel in the lattice has

- the corresponding layer value printed inside curly brackets, e.g.,
 '{1.12345}'

- the layer value printed in full

- the layer value rotated 90? CCW (like the y-axis label)

I would prefer to have

+ the layer value *not* printed inside curly brackets

+ the layer value *not* rotated 90? CCW (i.e., to print the layer
 value like the x-axis label)

+ the layer value truncated or rounded to some significant digits,
 e.g., '1.1'

https://stat.ethz.ch/pipermail/r-help/2012-November/329505.html

levelplot(
 conc ~ lon * lat | rev(lev), data=array.3d.df,
 layout=c(1,lev),   levs=as.character(round(array.3d.df[['lev']],  
1)),
 strip=FALSE,
 strip.left=strip.custom(
   factor.levels=as.character(round(array.3d.df[['lev']], 3)),
   strip.levels=TRUE,
   horizontal=TRUE,
   strip.names=FALSE ,
   par.strip.text=list( cex=0.5)
 )
)

...

Your example does not do a very good job of testing the levels
assignments since they are all the same.

Actually, that claim is false, as can be demonstrated in 2 ways:

1. (simple) Note column=lev in output from

head(array.3d.df)
tail(array.3d.df)

   The levels are not "all the same."

2. (more complex, but clearly demonstrates a flaw in the suggestion)
  Shorten the level values, then comment out the 'factor.levels'
  argument to strip.custom (above), and plot:

# shorten level values by 2 digits, for bug demonstration
array.3d.df$lev <- array.3d.df$lev - 0.00045
# note different output from these in column=lev
head(array.3d.df)
tail(array.3d.df)

# comment out for debugging
levelplot(
 conc ~ lon * lat | rev(lev), data=array.3d.df, layout=c(1,lev),
 levs=as.character(round(array.3d.df[['lev']], 1)),
 strip=FALSE,
 strip.left=strip.custom(
#    factor.levels=as.character(round(array.3d.df[['lev']], 3)),
   strip.levels=TRUE,
   horizontal=TRUE,
   strip.names=FALSE ,
   par.strip.text=list(cex=0.5)
 )
)

  Note that,

-  without the line above commented out, strip values are (correctly)
  all 1.123

+  with the line above commented out, strip values are (correctly)
  1.123 .. 5.123

Am I missing something? If not, how to round() or signif() the values
obtained from array.3d.df$lev and displayed in the strips?