genTable
creates a table of arbitrary summaries conditional on
given values of independent variables given by a formula.
Aggregate
does the same, but returns a data.frame
instead.
fapply
is a generic function that dispatches on its data
argument. It is called internally by Aggregate
and genTable
.
Methods for this function can be used to adapt Aggregate
and
genTable
to data sources other than data frames.
1 2 3 4 5 6 7 8 9 10 11  Aggregate(formula, data=parent.frame(), subset=NULL,
sort = TRUE, names=NULL, addFreq=TRUE, as.vars=1,
drop.constants=TRUE,...)
genTable(formula, data=parent.frame(), subset=NULL,
names=NULL, addFreq=TRUE,...)
fapply(formula,data,...) # calls UseMethod("fapply",data)
## Default S3 method:
fapply(formula, data, subset=NULL,
names=NULL, addFreq=TRUE,...)

formula 
a formula. The right hand side includes one or more grouping variables separated by '+'. These may be factors, numeric, or character vectors. The left hand side may be empty, a numerical variable, a factor, or an expression. See details below. 
data 
an environment or data frame or an object coercable into a data frame. 
subset 
an optional vector specifying a subset of observations to be used. 
sort 
a logical value; determines the order in which the aggregated
data appear in the data frame returned by 
names 
an optional character vector giving names to the
result(s) yielded by the expression on the left hand side of 
addFreq 
a logical value. If TRUE and

as.vars 
an integer; relevant only if the left hand side of the formula returns an array or a matrix  which dimension (rows, columns, or layers etc.) will transformed to variables? Defaults to columns in case of matrices and to the highest dimensional extend in case of arrays. 
drop.constants 
logical; variables that are constant across levels dropped from the result? 
... 
further arguments, passed to methods or ignored. 
If an expression is given as left hand side of the formula, its
value is computed for any combination of values of the values on the
right hand side. If the right hand side is a dot, then all
variables in data
are added to the right hand side of the
formula.
If no expression is given as left hand side, then the frequency counts for the respective value combinations of the right hand variables are computed.
If a single factor is on the left hand side, then the left hand side is
translated into an appropriate
call to table()
. Note that also in this case addFreq
takes effect.
If a single numeric variable is on the left hand side, frequency
counts weighted by this variable are computed. In these cases,
genTable
is equivalent to xtabs
and
Aggregate
is equivalent to as.data.frame(xtabs(...))
.
Aggregate
results in a data frame with conditional summaries and unique value combinations
of conditioning variables.
genTable
returns a table, that is, an array with class "table"
.
aggregate.data.frame, xtabs
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25  ex.data < expand.grid(mu=c(0,100),sigma=c(1,10))[rep(1:4,rep(100,4)),]
ex.data < within(ex.data,
x<rnorm(
n=nrow(ex.data),
mean=mu,
sd=sigma
)
)
Aggregate(~mu+sigma,data=ex.data)
Aggregate(mean(x)~mu+sigma,data=ex.data)
Aggregate(mean(x)~mu+sigma,data=ex.data,name="Average")
Aggregate(c(mean(x),sd(x))~mu+sigma,data=ex.data)
Aggregate(c(Mean=mean(x),StDev=sd(x),N=length(x))~mu+sigma,data=ex.data)
genTable(c(Mean=mean(x),StDev=sd(x),N=length(x))~mu+sigma,data=ex.data)
Aggregate(table(Admit)~.,data=UCBAdmissions)
Aggregate(Table(Admit,Freq)~.,data=UCBAdmissions)
Aggregate(Admit~.,data=UCBAdmissions)
Aggregate(percent(Admit)~.,data=UCBAdmissions)
Aggregate(percent(Admit)~Gender,data=UCBAdmissions)
Aggregate(percent(Admit)~Dept,data=UCBAdmissions)
Aggregate(percent(Gender)~Dept,data=UCBAdmissions)
Aggregate(percent(Admit)~Dept,data=UCBAdmissions,Gender=="Female")
genTable(percent(Admit)~Dept,data=UCBAdmissions,Gender=="Female")

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