Pseudo-function to compute a statistic relative to a reference set.

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

Usage

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 without any subsetting. (To pass a variable with subsetting, use the Arguments pseudo-function instead.)

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.

Examples

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"))))
#>                                           
#>          z                                
#>          E          F          All        
#>  x   y   All RowPct All RowPct All  RowPct
#>  A   c   118 50.64  115 49.36   233 100   
#>      d   139 54.30  117 45.70   256 100   
#>      All 257 52.56  232 47.44   489 100   
#>  B   c   132 50.77  128 49.23   260 100   
#>      d   127 50.60  124 49.40   251 100   
#>      All 259 50.68  252 49.32   511 100   
#>  All c   250 50.71  243 49.29   493 100   
#>      d   266 52.47  241 47.53   507 100   
#>      All 516 51.60  484 48.40  1000 100   
tabular( (x + 1)*(y + 1) ~ (z + 1)*(1+(xyPct=Percent(Equal(x, y)))))
#>                                        
#>          z                             
#>          E         F         All       
#>  x   y   All xyPct All xyPct All  xyPct
#>  A   c   118 50.64 115 49.36  233 100  
#>      d   139 54.30 117 45.70  256 100  
#>      All 257 52.56 232 47.44  489 100  
#>  B   c   132 50.77 128 49.23  260 100  
#>      d   127 50.60 124 49.40  251 100  
#>      All 259 50.68 252 49.32  511 100  
#>  All c   250 50.71 243 49.29  493 100  
#>      d   266 52.47 241 47.53  507 100  
#>      All 516 51.60 484 48.40 1000 100