memisc (version 0.97)

By: Conditional Evaluation of an Expression

Description

The function By evaluates an expression within subsets of a data frame, where the subsets are defined by a formula.

Usage

By(formula,expr,data=parent.frame())

Arguments

formula

an expression or (preferably) a formula containing the names of conditioning variables or factors.

expr

an expression that is evaluated for any unique combination of values of the variables contained in formula.

data

a data frame, an object that can be coerced into a data frame (for example, a table), or an environment, from which values for the variables in formula or expr are taken.

Value

• A list of class "by", giving the results for each combination of values of variables in formula.

Examples

berkeley <- Aggregate(Table(Admit,Freq)~.,data=UCBAdmissions)
(Bres <- By(~Dept,glm(cbind(Admitted,Rejected)~Gender,family="binomial"),data=berkeley))
# The results all have 'data' components
str(Bres[[1]]$data)

attach(berkeley)
(Bres <- By(~Dept,glm(cbind(Admitted,Rejected)~Gender,family="binomial")))
detach(berkeley)