# Percent: Pseudo-function to compute a statistic relative to a... In tables: Formula-Driven Table Generation

## Description

The `Percent` pseudo-function is used to specify a statistic that depends on other values in the table.

## Usage

 `1` ```Percent(denom = "all", fn = percent) ```

## Arguments

 `denom` How the reference set (the denominator in case of a percentage calculation) should be calculated. See below. `fn` The two argument function to calculate the statistic.

## Details

The function `fn` will be called with two arguments. The first argument is the usual “value vector” of values corresponding to this cell in the table, and the second is another vector of reference values, determined by `denom`.

The default value of `fn` is the `percent` function, defined as `function(x, y) 100*length(x)/length(y)`. This gives the ratio of the number of values in the current cell relative to the reference values, expressed as a percentage. Using `fn = function(x, y) 100*sum(x)/sum(y)` would give the percentage of the sum of the values in the current cell to the sum in the reference set.

With the default `denom = "all"`, all values of the analysis variable in the dataset are used as the reference. Other possibilities are `denom = "row"` or `denom = "col"`, for which the values of the variable corresponding to the current row or column subset are used.

The special syntax `denom = Equal(...)` will record each expression in `...`. The reference set will be the cases with equal values of all expressions in `...` to those of the current cell. The similar form `denom = Unequal(...)` sets the reference values to be those that differ in any of the `...` expressions from the current cell. (In fact, these can be used somewhat more generally; see the vignette for details.)

Finally, other possible `denom` values are a logical vector, in which case the values marked `TRUE` are used, or anything else, which will be passed to `fn` as `y`.

## Pseudo-functions

`Percent` is a “pseudo-function”: it takes the form of a function call, but is never actually called: it is handled specially by `tabular`. `Equal` and `Unequal` are also pseudo-functions, but are only special when used in the `denom` argument to `Percent`.

`Arguments` for a different way to specify a multiple argument analysis function.
 ```1 2 3 4 5 6 7``` ```x <- factor(sample(LETTERS[1:2], 1000, rep=TRUE)) y <- factor(sample(letters[3:4], 1000, rep=TRUE)) z <- factor(sample(LETTERS[5:6], 1000, rep=TRUE)) # These both do the same thing: tabular( (x + 1)*(y + 1) ~ (z + 1)*(1+(RowPct=Percent("row")))) tabular( (x + 1)*(y + 1) ~ (z + 1)*(1+(xyPct=Percent(Equal(x, y))))) ```