interaction {lattice}R Documentation

Functions to Interact with Lattice Plots


The classic Trellis paradigm is to plot the whole object at once, without the possibility of interacting with it afterwards. However, by keeping track of the grid viewports where the panels and strips are drawn, it is possible to go back to them afterwards and enhance them one panel at a time. These functions provide convenient interfaces to help in this. Note that these are still experimental and the exact details may change in future.


panel.identify(x, y = NULL,
               subscripts = seq_along(x),
               labels = subscripts, 
               n = length(x), offset = 0.5,
               threshold = 18, ## in points, roughly 0.25 inches
               panel.args = trellis.panelArgs(),
trellis.vpname(name = c("position", "split", "split.location", "toplevel",
               "panel", "strip", "strip.left", "legend",
               "main", "sub", "xlab", "ylab", "page"),
               column, row,
               side = c("left", "top", "right", "bottom", "inside"),
      = FALSE, prefix)
trellis.grobname(name, prefix)
trellis.focus(name, column, row, side,,
              highlight = interactive(), ...)
trellis.switchFocus(name, side,, highlight, ...)
trellis.panelArgs(x, packet.number)


x, y variables defining the contents of the panel. In the case of trellis.panelArgs, a "trellis" object.
n the number of points to identify by default (overridden by a right click)
subscripts an optional vector of integer indices associated with each point. See details below.
labels an optional vector of labels associated with each point. Defaults to subscripts
offset the labels are printed either below, above, to the left or to the right of the identified point, depending on the relative location of the mouse click. The offset specifies (in "char" units) how far from the identified point the labels should be printed.
threshold threshold in grid's "points" units. Points further than these from the mouse click position are not considered
panel.args list that contains components names x (and usually y), to be used if x is missing. Typically, when called after trellis.focus, this would appropriately be the arguments passed to that panel.
name character string indicating which viewport or grob we are looking for. Although these do not necessarily provide access to all viewports and grobs created by a lattice plot, they cover most that users might find interesting.
trellis.vpname and trellis.focus deal with viewport names only, and only accept the values explicitly listed above. trellis.grobname is meant to create names for grobs, and can currently accept any value.
column, row integers, indicating position of the panel or strip that should be assigned focus in the Trellis layout. Rows are usually calculated from the bottom up, unless the plot was created with as.table=TRUE
side character string, relevant only for legends (i.e. when name="legend"), indicating their position. Partial specification is allowed, as long as it is unambiguous. logical, whether clipping should be off, relevant when name is "panel" or "strip". This is necessary if axes are to be drawn outside the panel or strip. Note that setting does not necessarily mean that clipping is on; that is determined by conditions in effect during printing.
prefix character string acting as a prefix, meant to distinguish otherwise equivalent viewports in different plots. This only becomes relevant when a particular page is occupied by more than one plot. Defaults to the value appropriate for the last "trellis" object printed, as determined by the prefix argument in print.trellis. Users should not usually need to supply a value for this argument (see note below), however, if supplied explicitly, this has to be a valid R symbol name (briefly, it must start with a letter or a period followed by a letter) and must not contain the grid path separator (currently "::")
highlight logical, whether the viewport being assigned focus should be highlighted. For trellis.focus, the default is TRUE in interactive mode, and trellis.switchFocus by default preserves the setting currently active.
packet.number integer, which panel to get data from. See packet.number for details on how this is calculated
... graphical parameters. For panel.identify these are used for labelling. For trellis.focus and trellis.switchFocus, these are used (in combination with lattice.options) for highlighting the chosen viewport if so requested.


panel.identify is similar to identify. When called, it waits for the user to identify points (in the panel being drawn) via mouse clicks. Clicks other than left-clicks terminate the procedure. Although it is possible to call it as part of the panel function, it is more typical to use it to identify points after plotting the whole object, in which case a call to trellis.focus first is necessary.

One way in which panel.identify is different from identify is in how it uses the subscripts argument. In general, when one identifies points in a panel, one wants to identify the origin in the data frame used to produce the plot, and not within that particular panel. This information is available to the panel function, but only in certain situations. One way to ensure that subscripts is available is to specify subscripts = TRUE in the high level call such as xyplot. If subscripts is not explicitly specified in the call to panel.identify, but is available in panel.args, then those values will be used. Otherwise, they default to seq_along(x). In either case, the final return value will be the subscripts that were marked.

The process of printing (plotting) a Trellis object builds up a grid layout with named viewports which can then be accessed to modify the plot further. While full flexibility can only be obtained by using grid functions directly, a few lattice functions are available for the more common tasks.

trellis.focus can be used to move to a particular panel or strip, identified by its position in the array of panels. It can also be used to focus on the viewport corresponding to one of the labels or a legend, though such usage would be less useful. The exact viewport is determined by the name along with the other arguments, not all of which are relevant for all names. Note that when more than one object is plotted on a page, trellis.focus will always go to the plot that was created last. For more flexibility, use grid functions directly (see note below).

After a successful call to trellis.focus, the desired viewport (typically panel or strip area) will be made the ‘current’ viewport (plotting area), which can then be enhanced by calls to standard lattice panel functions as well as grid functions.

It is quite common to have the layout of panels chosen when a "trellis" object is drawn, and not before then. Information on the layout (specifically, how many rows and columns, and which packet belongs in which position in this layout) is retained for the last "trellis" object plotted, and is available through trellis.currentLayout.

trellis.unfocus unsets the focus, and makes the top level viewport the current viewport.

trellis.switchFocus is a convenience function to switch from one viewport to another, while preserving the current row and column. Although the rows and columns only make sense for panels and strips, they would be preserved even when the user switches to some other viewport (where row/column is irrelevant) and then switches back.

Once a panel or strip is in focus, trellis.panelArgs can be used to retrieve the arguments that were available to the panel function at that position. In this case, it can be called without arguments as


This usage is also allowed when a "trellis" object is being printed, e.g. inside the panel functions or the axis function (but not inside the prepanel function). trellis.panelArgs can also retrieve the panel arguments from any "trellis" object. Note that for this usage, one needs to specify the packet.number (as described under the panel entry in xyplot) and not the position in the layout, because a layout determines the panel only after the object has been printed.

It is usually not necessary to call trellis.vpname and trellis.grobname directly. However, they can be useful in generating appropriate names in a portable way when using grid functions to interact with the plots directly, as described in the note below.


panel.identify returns an integer vector containing the subscripts of the identified points (see details above). The equivalent of identify with pos=TRUE is not yet implemented, but can be considered for addition if requested.
trellis.panelArgs returns a named list of arguments that were available to the panel function for the chosen panel.
trellis.vpname and trellis.grobname return character strings.


The viewports created by lattice is accessible to the user only up to a certain extent, as described above. In particular, trellis.focus can only be used to manipulate the last plot drawn. For full flexibility, use appropriate functions from the grid package directly. For example, current.vpTree can be used to inspect the current viewport tree and seekViewport or downViewport can be used to navigate to these viewports. For such usage, trellis.vpname and trellis.grobname (with a non-default prefix argument) provides a portable way to access the appropriate viewports and grobs by name.


Deepayan Sarkar

See Also

identify, Lattice, print.trellis, trellis.currentLayout, current.vpTree, viewports


## Not run: 
xyplot(1:10 ~ 1:10)
trellis.focus("panel", 1, 1)
## End(Not run)

xyplot(Petal.Length ~ Sepal.Length | Species, iris, layout = c(2, 2))

trellis.focus("panel", 1, 1)"panel.lmline", trellis.panelArgs())

trellis.focus("panel", 2, 1)"panel.lmline", trellis.panelArgs())

trellis.focus("panel", 1, 2)"panel.lmline", trellis.panelArgs())

## choosing loess smoothing parameter

p <- xyplot(dist ~ speed, cars)

panel.loessresid <-
    function(x = panel.args$x,
             y = panel.args$y,
             panel.args = trellis.panelArgs())
    fm <- loess(y ~ x, span = span)
    xgrid <- do.breaks(current.panel.limits()$xlim, 50)
    ygrid <- predict(fm, newdata = data.frame(x = xgrid))
    panel.lines(xgrid, ygrid)
    pred <- predict(fm)
    ## center residuals so that they fall inside panel
    resids <- y - pred + mean(y)
    fm.resid <- loess.smooth(x, resids, span = span)
    ##panel.points(x, resids, col = 1, pch = 4)
    panel.lines(fm.resid, col = 1)

spans <- c(0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8)
update(p, index.cond = list(rep(1, length(spans))))
panel.locs <- trellis.currentLayout()

i <- 1

for (row in 1:nrow(panel.locs))
    for (column in 1:ncol(panel.locs))
    if (panel.locs[row, column] > 0)
    trellis.focus("panel", row = row, column = column,
                  highlight = FALSE)
    panel.loessresid(span = spans[i])
    grid::grid.text(paste("span = ", spans[i]),
                    x = 0.25,
                    y = 0.75,
                    default.units = "npc")
    i <- i + 1

[Package lattice version 0.15-4 Index]