Extracts the prototype from each variable group.

## Usage

`proto(X, y, groups, type = c("max", "median"), mu = NULL)`

## Arguments

- X
Predictor matrix.

- y
Response matrix with one column.

- groups
An group index vector containing the group number each variable belongs to. For example:

`c(1, 1, 1, 1, 1, 2, 2, 2, ...)`

. Variable groups can be generated by the Fisher optimal partition algorithm implemented in`FOP()`

.- type
The rule for extracting the prototype. Possible options are

`"max"`

and`"median"`

.- mu
The mean value of

`y`

for standardization. Default is`NULL`

, which uses the sample mean of`y`

.