Calculates banking slope

`banking(dx, dy)`

dx, dy

vector of consecutive x, y differences.

`banking`

is the banking function used when
`aspect = "xy"`

in high level Trellis functions. It is usually not
very meaningful except with `xyplot`

. It considers the
absolute slopes (based on `dx`

and `dy`

) and returns a value
which when adjusted by the panel scale limits will make the median of
the above absolute slopes correspond to a 45 degree line.

This function was inspired by the discussion of banking in the
documentation for Trellis Graphics available at Bell Labs' website
(see `Lattice`

), but is most likely identical to an
algorithm described by Cleveland et al (see below). It is
not clear (to the author) whether this is the algorithm used in
S-PLUS. Alternative banking rules, implemented as a similar function,
can be used as a drop-in replacement by suitably modifying
`lattice.options("banking")`

.

Cleveland, William S. and McGill, Marylyn E. and McGill, Robert (1988)
“The Shape Parameter of a Two-variable Graph”, *Journal of
the American Statistical Association*, **83**, 289--300.

# NOT RUN { ## with and without banking plot <- xyplot(sunspot.year ~ 1700:1988, xlab = "", type = "l", scales = list(x = list(alternating = 2)), main = "Yearly Sunspots") print(plot, position = c(0, .3, 1, .9), more = TRUE) print(update(plot, aspect = "xy", main = "", xlab = "Year"), position = c(0, 0, 1, .3)) ## cut-and-stack plot (see also xyplot.ts) xyplot(sunspot.year ~ time(sunspot.year) | equal.count(time(sunspot.year)), xlab = "", type = "l", aspect = "xy", strip = FALSE, scales = list(x = list(alternating = 2, relation = "sliced")), as.table = TRUE, main = "Yearly Sunspots") # }