By | R Documentation |

The function `By`

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

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

`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 |

`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 |

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

.

```
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)
```

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