R: Structured Displays of Contingency Tables

strucplot {vcd} | R Documentation

## Structured Displays of Contingency Tables

### Description

This modular function visualizes certain aspects of high-dimensional contingency tables in a hierarchical way.

### Usage

    strucplot(x, residuals = NULL, expected = NULL,
      condvars = NULL, shade = NULL, type = c("observed", "expected"),
      residuals_type = NULL, df = NULL, split_vertical = NULL,
      spacing = spacing_equal, spacing_args = list(),
      gp = NULL, gp_args = list(),
      labeling = labeling_border, labeling_args = list(),
      core = struc_mosaic, core_args = list(),
      legend = NULL, legend_args = list(),
      main = NULL, sub = NULL, margins = unit(3, "lines"),
      title_margins = NULL, legend_width = NULL,
      main_gp = gpar(fontsize = 20), sub_gp = gpar(fontsize = 15),
      newpage = TRUE, pop = TRUE, return_grob = FALSE,
      keep_aspect_ratio = NULL, prefix = "", ...)

### Arguments

`x` | a contingency table in array form, with optional category labels specified in the `dimnames` attribute.
`residuals` | optionally, an array of residuals of the same dimension as `x` (see details).
`expected` | optionally, an array of expected values of the same dimension as `x`, or alternatively the corresponding independence model specification as used by `loglin` or `loglm` (see details).
`df` | degrees of freedom passed to the shading functions used for inference. Will be calculated (and overwritten if specified) if both `expected` and `residuals` are `NULL`, or if `expected` is given a formula.
`condvars` | number of conditioning variables, if any; those are expected to be ordered first in the table. This information is used for computing the expected values, and is also passed to the spacing functions (see `spacings`).
`shade` | logical specifying whether `gp` should be used or not (see `gp`). If `TRUE` and `expected` is unspecified, a default model is fitted: if `condvars` is specified, a corresponding conditional independence model, and else the total independence model.
`residuals_type` | a character string indicating the type of residuals to be computed when none are supplied. If `residuals` is `NULL`, `residuals_type` must be one of `"pearson"` (default; giving components of Pearson's chi-squared), `"deviance"` (giving components of the likelihood ratio chi-squared), or `"FT"` for the Freeman-Tukey residuals. The value of this argument can be abbreviated. If `residuals` are specified, the value of `residuals_type` is just passed “as is” to the legend function.
`type` | a character string indicating whether the observed or the expected values of the table should be visualized.
`split_vertical` | vector of logicals of length k, where k is the number of margins of `x` (values are recycled as needed). A `TRUE` component indicates that the tile(s) of the corresponding dimension should be split vertically, `FALSE` means horizontal splits. Default is `FALSE.`
`spacing` | spacing object, spacing function, or a corresponding generating function (see details and `spacings`).
`spacing_args` | list of arguments for the spacing-generating function, if specified.
`gp` | object of class `"gpar"`, shading function or a corresponding generating function (see details and `shadings`). Components of `"gpar"` objects are recycled as needed along the last splitting dimension. Ignored if `shade = FALSE`.
`gp_args` | list of arguments for the shading-generating function, if specified.
`labeling` | either a logical, or a labeling function, or a corresponding generating function (see details and `labelings`. If `FALSE` or `NULL`, no labeling is produced.
`labeling_args` | list of arguments for the labeling-generating function, if specified.
`core` | either a core function, or a corresponding generating function (see details). Currently, generating functions for mosaic plots (`struc_mosaic`), association plots (`struc_assoc`), and sieve plots (`struc_sieve`) are provided.
`core_args` | list of arguments for the core-generating function, if specified.
`legend` | either a legend-generating function, or a legend function (see details and `legends`), or a logical. If `legend` is `NULL` or `TRUE` and `gp` is a function, legend defaults to `legend_resbased`.
`legend_args` | list of arguments for the legend-generating function, if specified.
`main` | either a logical, or a character string used for plotting the main title. If `main` is a logical and `TRUE`, the name of the object supplied as `x` is used.
`sub` | a character string used for plotting the subtitle. If `sub` is a logical and `TRUE` and `main` is unspecified, the name of the object supplied as `x` is used.
`margins` | either an object of class `"unit"` of length 4, or a numeric vector of length 4. The elements are recycled as needed. The four components specify the top, right, bottom, and left margin of the plot, respectively. When a numeric vector is supplied, the numbers are interpreted as `"lines"` units. In addition, the unit or numeric vector may have named arguments (top, right, bottom, and left), in which case the non-named arguments specify the default values (recycled as needed), overloaded by the named arguments.
`title_margins` | either an object of class `"unit"` of length 2, or a numeric vector of length 2. The elements are recycled as needed. The two components specify the top and bottom title margin of the plot, respectively. The default for each specified title are 2 lines (and 0 else), except when a legend is plotted and `keep_aspect_ratio` is `TRUE`: in this case, the default values of both margins are set as to align the heights of legend and actual plot. When a numeric vector is supplied, the numbers are interpreted as `"lines"` units. In addition, the unit or numeric vector may have named arguments (top and bottom), in which case the non-named argument specify the default value (recycled as needed), overloaded by the named arguments.
`legend_width` | An object of class `"unit"` of length 1 specifying the width of the legend (if any). Default: 5 lines.
`pop` | logical indicating whether the generated viewport tree should be removed at the end of the drawing or not.
`main_gp, sub_gp` | object of class `"gpar"` containing the graphical parameters used for the main (sub) title, if specified.
`newpage` | logical indicating whether a new page should be created for the plot or not.
`return_grob` | logical. Should a snapshot of the display be returned as a grid grob?
`keep_aspect_ratio` | logical indicating whether the aspect ratio should be fixed or not. If unspecified, the default is `TRUE` for two-dimensional tables and `FALSE` otherwise.
`prefix` | optional character string used as a prefix for the generated viewport and grob names.
`...` | For convenience, list of arguments passed to the labeling-generating function used.

### Details

This function—usually called by higher-level functions such as `assoc` and `mosaic`—generates conditioning plots of contingency tables. First, it sets up a set of viewports for main- and subtitles, legend, and the actual plot region. Then, residuals are computed as needed from observed and expected frequencies, where the expected frequencies are optionally computed for a specified independence model. Finally, the specified functions for spacing, gp, main plot, legend, and labeling are called to produce the plot. The function invisibly returns the `"structable"` object visualized.

Most elements of the plot, such as the core function, the spacing between the tiles, the shading of the tiles, the labeling, and the legend, are modularized in graphical appearance control (“grapcon”) functions and specified as parameters. For each element foo (= `spacing`, `labeling`, `core`, or `legend`), `strucplot` takes two arguments: foo and foo\_args, which can be used to specify the parameters in the following alternative ways:

1. Passing a suitable function to foo which subsequently will be called from `strucplot` to compute shadings, labelings, etc.

2. Passing a corresponding generating function to foo, along with parameters passed to foo\_args, that generates such a function. Generating functions must inherit from classes `"grapcon_generator"` and `"}foo\code{"`.

3. Except for the shading functions (shading\_bar), passing foo(foo\_args) to the foo argument.

4. For shadings and spacings, passing the final parameter object itself; see the corresponding help pages for more details on the data structures.

If legends are drawn, a ‘cinemascope’-like layout is used for the plot to preserve the 1:1 aspect ratio.

If `type = "expected"`, the expected values are passed to the `observed` argument of the core function, and the observed values to the `expected` argument.

Although the `gp` argument is typically used for shading, it can be used for arbitrary modifications of the tiles' graphics parameters (e.g., for highlighting particular cells, etc.).

### Value

Invisibly, an object of class `"structable"` corresponding to the plot. If `return_grob` is `TRUE`, additionally, the plot as a grob object is returned in a `grob` attribute.

### Note

The created viewports, as well as the tiles and bullets, are named and thus can conveniently modified after a plot has been drawn (and `pop = FALSE`).

### Author(s)

David Meyer David.Meyer@R-project.org

### References

Meyer D., Zeileis A., and Hornik K. (2006), The strucplot framework: Visualizing multi-way contingency tables with vcd. Journal of Statistical Software, 17(3), 1-48. URL http://www.jstatsoft.org/v17/i03/ and available as `vignette("strucplot")`.

### See Also

`assoc`, `mosaic`, `sieve`, `struc_assoc`, `struc_sieve`, `struc_mosaic`, `structable`, `doubledecker`, `labelings`, `shadings`, `legends`, `spacings`

### Examples

    data("Titanic")

    strucplot(Titanic)
    strucplot(Titanic, core = struc_assoc)
    strucplot(Titanic, spacing = spacing_increase,
                       spacing_args = list(start = 0.5, rate = 1.5))
    strucplot(Titanic, spacing = spacing_increase(start = 0.5, rate = 1.5))

    ## modify a tile's color
    strucplot(Titanic, pop = FALSE)
    grid.edit("rect:Class=1st,Sex=Male,Age=Adult,Survived=Yes",
              gp = gpar(fill = "red"))

[Package vcd version 1.4-4 Index]