# U: Create a Transformed Variable In uwIntroStats: Descriptive Statistics, Inference, Regression, and Plotting in an Introductory Statistics Course

## Description

Creates a transformed variable using either the natural log, a dummy transformation, linear splines, or a polynomial. Mostly for use in regression. If a partial formula of the form `~var1 + var2` is entered, returns the formula for use in regression. The partial formula can be named by adding an equals sign before the tilde.

## Usage

 ```1 2 3``` ```U(..., type=NULL, subset=rep(T,length(x)), knots=NULL, degree=2, reference=sort(unique(x[!is.na(x)])), lbl=NULL, center=mean(x,na.rm=T), includeAll=FALSE, parameterization="absolute", vrsn=FALSE) ```

## Arguments

 `...` variable(s) used to create the transformation. `type` a character string describing the transformation. Partial matching is used, so only enough of the string to make the transformation unique is needed. `subset` used in creating dummy variables. Only used if `type == "dummy"`. `knots` vector of knots to create the splines. Only used if `type=="lspline"`. `degree` the degree of the polynomial to be returned. Only used if `type=="polynomial"`. `reference` the reference vector for levels of the dummy variable. Only used if `type=="dummy"`. `lbl` a label for the splines. Only used if `type=="lspline"` `center` the center of the returned polynomial. Only used if `type=="polynomial"`. `includeAll` a logical value to use all values even in the presense of a subset. Only used if `type=="dummy"`. `parameterization` defaults to`"absolute"`, and provides splines based on the absolute slope between knots. If `"change"`, provides splines based on the change from knot to knot. If `lsplineD` is called, `"change"` is entered by default. Only used if `type=="lspline"`. `vrsn` if `TRUE`, returns the version of the function and nothing else.

## Value

A matrix or vector containing the transformations. The class of the returned value is `c("transformation", y)` where `y` is the class of the transformed variable (usually `numeric`). The type of transformation performed is encoded as one of the attributes of the returned value, along with the original data.

## Author(s)

Scott S. Emerson, M.D., Ph.D., Andrew J. Spieker, Brian D. Williamson

## See Also

`regress`

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15``` ```# Reading in a dataset mri <- read.table("http://www.emersonstatistics.com/datasets/mri.txt", header=TRUE) attach(mri) # Create a spline based on absolute U(ldl, type="lspline", knots=c(70, 100, 130, 160)) U(ldl, type="ls", knots=c(70,100,130,160)) # Create a spline based on change U(ldl, type="ls", knots=c(70, 100, 130, 160), parameterization="change") # Create a log transformed variable U(age, type="log") ## Create a partial formula U(ma=~male+age) ```

uwIntroStats documentation built on Oct. 10, 2018, 5:04 p.m.