# By

From memisc v0.99.27.3
by Martin Elff

##### Conditional Evaluation of an Expression

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

```
# NOT RUN {
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)
# }
```

*Documentation reproduced from package memisc, version 0.99.27.3, License: GPL-2*

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