R: Formula Notation for Flat Contingency Tables

ftable.formula {base} | R Documentation

## Formula Notation for Flat Contingency Tables

### Description

Produce or manipulate a flat contingency table using formula notation.

### Usage

    ftable(formula, data = NULL, subset, na.action, ...)

### Arguments

`formula` | a formula object with 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 a contingency table (see below).
`subset` | an optional vector specifying a subset of observations to be used. Ignored if `data` is a contingency table.
`na.action` | a function which indicates what should happen when the data contain `NA`s. Ignored if `data` is a contingency table.
`...` | further arguments to the default ftable method may also be passed as arguments, see `ftable.default`.

### Details

This is a method of the generic function `ftable`.

The left and right hand side of `formula` specify the column and row variables, respectively, of the flat contingency table to be created. Only the `+` operator is allowed for combining the variables. A `.` may be used once in the formula to indicate inclusion of all the ``remaining'' variables.

If `data` is an object of class `"table"` or an array with more than 2 dimensions, it is taken as a contingency table, and hence all entries should be nonnegative. Otherwise, if it is not a flat contingency table (i.e., an object of class `"ftable"`), it should be a data frame or matrix, list or environment containing the variables to be cross-tabulated. In this case, `na.action` is applied to the data to handle missing values, and, after possibly selecting a subset of the data as specified by the `subset` argument, a contingency table is computed from the variables.

The contingency table is then collapsed to a flat table, according to the row and column variables specified by `formula`.

### Value

A flat contingency table which contains the counts of each combination of the levels of the variables, collapsed into a matrix for suitably displaying the counts.

### See Also

`ftable`, `ftable.default`; `table`.

### Examples

    data(Titanic)
    Titanic
    x <- ftable(Survived ~ ., data = Titanic)
    x
    ftable(Sex ~ Class + Age, data = x)

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