# assoc

##### Extended Association Plots

Produce an association plot indicating deviations from a specified independence model in a possibly high-dimensional contingency table.

- Keywords
- hplot

##### Usage

```
# S3 method for default
assoc(x, row_vars = NULL, col_vars = NULL, compress = TRUE,
xlim = NULL, ylim = NULL,
spacing = spacing_conditional(sp = 0), spacing_args = list(),
split_vertical = NULL, keep_aspect_ratio = FALSE,
xscale = 0.9, yspace = unit(0.5, "lines"), main = NULL, sub = NULL,
…, residuals_type = "Pearson", gp_axis = gpar(lty = 3))
# S3 method for formula
assoc(formula, data = NULL, …, subset = NULL, na.action = NULL, main = NULL, sub = NULL)
```

##### Arguments

- x
a contingency table in array form with optional category labels specified in the

`dimnames(x)`

attribute, or an object inheriting from the`"ftable"`

class (such as`"structable"`

objects).- row_vars
a vector of integers giving the indices, or a character vector giving the names of the variables to be used for the rows of the association plot.

- col_vars
a vector of integers giving the indices, or a character vector giving the names of the variables to be used for the columns of the association plot.

- compress
logical; if

`FALSE`

, the space between the rows (columns) are chosen such that the*total*heights (widths) of the rows (columns) are all equal. If`TRUE`

, the space between rows and columns is fixed and hence the plot is more “compressed”.- xlim
a \(2 \times k\) matrix of doubles, \(k\) number of total columns of the plot. The columns of

`xlim`

correspond to the columns of the association plot, the rows describe the column ranges (minimums in the first row, maximums in the second row). If`xlim`

is`NULL`

, the ranges are determined from the residuals according to`compress`

(if`TRUE`

: widest range from each column, if`FALSE`

: from the whole association plot matrix).- ylim
a \(2 \times k\) matrix of doubles, \(k\) number of total rows of the plot. The columns of

`ylim`

correspond to the rows of the association plot, the rows describe the column ranges (minimums in the first row, maximums in the second row). If`ylim`

is`NULL`

, the ranges are determined from the residuals according to`compress`

(if`TRUE`

: widest range from each row, if`FALSE`

: from the whole association plot matrix).- spacing
a spacing object, a spacing function, or a corresponding generating function (see

`strucplot`

for more information). The default is the spacing-generating function`spacing_conditional`

that is (by default) called with the argument list`spacing_args`

(see`spacings`

for more details).- spacing_args
list of arguments for the spacing-generating function, if specified (see

`strucplot`

for more information).- split_vertical
vector of logicals of length \(k\), where \(k\) is the number of margins of

`x`

(default:`FALSE`

). Values are recycled as needed. A`TRUE`

component indicates that the corresponding dimension is folded into the columns,`FALSE`

folds the dimension into the rows.- keep_aspect_ratio
logical indicating whether the aspect ratio should be fixed or not.

- residuals_type
a character string indicating the type of residuals to be computed. Currently, only Pearson residuals are supported.

- xscale
scale factor resizing the tile's width, thus adding additional space between the tiles.

- yspace
object of class

`"unit"`

specifying additional space separating the rows.- gp_axis
object of class

`"gpar"`

specifying the visual aspects of the tiles' baseline.- formula
a formula object with possibly both left and right hand sides specifying the column and row variables of the flat table.

- data
a data frame, list or environment containing the variables to be cross-tabulated, or an object inheriting from class

`table`

.- subset
an optional vector specifying a subset of observations to be used. Ignored if

`data`

is a contingency table.- na.action
an optional function which indicates what should happen when the data contain

`NA`

s. Ignored if`data`

is a contingency table.- main, sub
either a logical, or a character string used for plotting the main (sub) title. If logical and

`TRUE`

, the name of the`data`

object is used.- …
other parameters passed to

`strucplot`

##### Details

Association plots have been suggested by Cohen (1980) and extended by Friendly (1992) and provide a means for visualizing the residuals of an independence model for a contingency table.

`assoc`

is a generic function and currently has a default method and a
formula interface. Both are high-level interfaces to the
`strucplot`

function, and produce (extended) association
plots. Most of the functionality is described there, such as
specification of the independence model, labeling, legend, spacing,
shading, and other graphical parameters.

For a contingency table, the signed contribution to Pearson's \(\chi^2\) for cell \(\{ij\ldots k\}\) is

$$d_{ij\ldots k} = \frac{(f_{ij\ldots k} - e_{ij\ldots k})}{ \sqrt{e_{ij\ldots k}}}$$

where \(f_{ij\ldots k}\) and \(e_{ij\ldots k}\) are the observed and expected counts corresponding to the cell. In the association plot, each cell is represented by a rectangle that has (signed) height proportional to \(d_{ij\ldots k}\) and width proportional to \(\sqrt{e_{ij\ldots k}}\), so that the area of the box is proportional to the difference in observed and expected frequencies. The rectangles in each row are positioned relative to a baseline indicating independence (\(d_{ij\ldots k} = 0\)). If the observed frequency of a cell is greater than the expected one, the box rises above the baseline, and falls below otherwise.

Additionally, the residuals can be colored depending on a specified
shading scheme (see Meyer et al., 2003). Package vcd offers a range of
*residual-based* shadings (see the shadings help page). Some of
them allow, e.g., the visualization of test statistics.

Unlike the `assocplot`

function in the
graphics package, this function allows the visualization of
contingency tables with more than two dimensions. Similar to the
construction of ‘flat’ tables (like objects of class `"ftable"`

or
`"structable"`

), the dimensions are folded into rows and columns.

The layout is very flexible: the specification of shading, labeling,
spacing, and legend is modularized (see `strucplot`

for
details).

##### Value

The `"structable"`

visualized is returned invisibly.

##### References

Cohen, A. (1980),
On the graphical display of the significant components in a two-way
contingency table.
*Communications in Statistics---Theory and Methods*, **A9**,
1025--1041.

Friendly, M. (1992),
Graphical methods for categorical data.
*SAS User Group International Conference Proceedings*, **17**,
190--200.
http://datavis.ca/papers/sugi/sugi17.pdf

Meyer, D., Zeileis, A., Hornik, K. (2003), Visualizing independence using
extended association plots. *Proceedings of the 3rd International
Workshop on Distributed Statistical Computing*, K. Hornik, F. Leisch,
A. Zeileis (eds.), ISSN 1609-395X.
https://www.R-project.org/conferences/DSC-2003/Proceedings/

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

##### Examples

```
# NOT RUN {
data("HairEyeColor")
## Aggregate over sex:
(x <- margin.table(HairEyeColor, c(1, 2)))
## Ordinary assocplot:
assoc(x)
## and with residual-based shading (of independence)
assoc(x, main = "Relation between hair and eye color", shade = TRUE)
## Aggregate over Eye color:
(x <- margin.table(HairEyeColor, c(1, 3)))
chisq.test(x)
assoc(x, main = "Relation between hair color and sex", shade = TRUE)
# Visualize multi-way table
assoc(aperm(HairEyeColor), expected = ~ (Hair + Eye) * Sex,
labeling_args = list(just_labels = c(Eye = "left"),
offset_labels = c(right = -0.5),
offset_varnames = c(right = 1.2),
rot_labels = c(right = 0),
tl_varnames = c(Eye = TRUE))
)
assoc(aperm(UCBAdmissions), expected = ~ (Admit + Gender) * Dept, compress = FALSE,
labeling_args = list(abbreviate = c(Gender = TRUE), rot_labels = 0)
)
# }
```

*Documentation reproduced from package vcd, version 1.4-5, License: GPL-2*