Generate Strip Labels

USAGE:

strip.default(which.given, which.panel, var.name, 
              factor.levels, shingle.intervals, 
              par.strip.text = trellis.par.get("add.text"), 
              strip.names = c(F, T), style = 3, strip.var.names = NULL) 

ARGUMENTS:

which.given
integer that tells which of the variables the current strip label corresponds to.
which.panel
integer vector that tells the levels of each of the given variables. which.panel[which.given] is the level of the current factor or shingle.
var.name
character vector giving the names of all of the given variables. var.name[which.given] is the name of the current variable.
factor.levels
if variable for this strip label is a factor, this argument gives the character string of all of the levels; otherwise it is NULL. The current level of the current factor is factor.levels[which.panel[which.given]].
shingle.intervals
if variable for this strip label is a shingle, this argument gives the matrix of intervals; otherwise it is NULL. The current interval of the current shingle is shingle.intervals[which.panel[which.given],]. The intervals have been scaled to range from 0 to 1.
par.strip.text
a list giving graphical parameters that should be in effect when the text is drawn in the strip labels.
strip.names
logical vector of length 2 (for factors and shingles, respectively) that tells whether the variable name should be put in the strip label. The first element indicates whether the names of factors should be included in strip labels along with the names of factor levels. The second element indicates whether the names of shingles should be included.
style
a numeric variable that tells which style should be used for strip labels corresponding to factors. For particular situations (e.g. factors where the names of all of the levels can be plotted in a strip label), some of the less-common styles may be very effective. Current styles include: 1 = the full strip label is colored in background color and the text string for the current factor level is centered in it; 2 = all the factor levels are spread across the strip with the current level is drawn atop a colored rectangle; 3 = identical to style 1 but a portion of the strip is highlighted (as in a shingle) to indicate the position of the current level; 4 = like 2 except the entire strip label is colored in background color. 5 = like 1 but the current factor level is positioned left-to-right across the strip; 6 = like 5 but the string adjustment varies from left-justified to right-justified as the string moves left-to-right.
The strip function is called once for each strip label on each panel. When it is called, both the x- and y-coordinates are set up from 0 to 1. If you are bold enough, you can modify strip.default to add your own styles or you can write your own strip function.
strip.var.names
a character vector containing strings to use for labeling strips, instead of using the default variable names. The length of strip.var.names should equal the length of var.name, and the order of the strings in strip.var.names should correspond to the variable names in var.name. The first element of the strip.names must be TRUE, for example strip.names=c(T,T).

EXAMPLES:

# use a non-standard strip style for factors 
xyplot(..., strip = function(...) strip.default(..., style = 2)) 

# create a boxplot using strip.default
bwplot(age ~ log(1 + usage) | income * pick, strip = function(...)
   strip.default(..., strip.names = c(T, T), strip.var.names = c("Income Level",
   "Long Distance Phone Service")), skip = c(F, F, F, F, F, F, F, T),
   layout = c(2, 4, 2), data = market.survey)