interaction {lattice} | R Documentation

## Functions to Interact with Lattice Plots

### Description

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.

### Usage

    panel.identify(x, y = NULL, labels = seq(along = x),
                   n = length(x), offset = 0.5,
                   threshold = 18,
                   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"),
                   clip.off = FALSE, prefix)
    trellis.grobname(name, prefix)
    trellis.focus(name, column, row, side, clip.off,
                  highlight = interactive(), ...)
    trellis.switchFocus(name, side, clip.off, highlight, ...)
    trellis.unfocus()
    trellis.panelArgs(x, packet.number)
    trellis.panelArgs()
    trellis.currentLayout()

### Arguments

`x, y` | variables defining the contents of the panel
`n` | the number of points to identify by default (overridden by a right click)
`labels` | an optional vector of labels associated with each point.
`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.
`clip.off` | 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 `clip.off=FALSE` 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 `xyplot` 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.

### Details

`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.

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. `trellis.panelArgs` can also, more generally, retrieve the panel arguments from any `"trellis"` object. Note that for this usage, one needs to specify the `panel.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.

### Value

`panel.identify` returns an integer vector containing the indexes of the identified points. The equivalent of `identify` with `pos=TRUE` is not yet implemented, but can be considered for addition if requested.
`trellis.currentLayout` returns a matrix with as many rows and columns as in the layout of panels in the last plot. Entries in the matrix are integer indices indicating which packet (panel data) occupies that position, with 0 indicating the absence of a panel.
`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.

### Note

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.

### Author(s)

Deepayan Sarkar Deepayan.Sarkar@R-project.org

### See Also

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

### Examples

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

    xyplot(Petal.Length ~ Sepal.Length | Species, iris, layout = c(2, 2))
    Sys.sleep(1)

    trellis.focus("panel", 1, 1)
    do.call("panel.lmline", trellis.panelArgs())
    Sys.sleep(0.5)
    trellis.unfocus()

    trellis.focus("panel", 2, 1)
    do.call("panel.lmline", trellis.panelArgs())
    Sys.sleep(0.5)
    trellis.unfocus()

    trellis.focus("panel", 1, 2)
    do.call("panel.lmline", trellis.panelArgs())
    Sys.sleep(0.5)
    trellis.unfocus()

    ## choosing loess smoothing parameter

    p <- xyplot(dist ~ speed, cars)

    panel.loessresid <-
        function(x = panel.args$x,
                 y = panel.args$y,
                 span,
                 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")
        trellis.unfocus()
        i <- i + 1
    }

[Package lattice version 0.13-8 Index]