# dummy.code

##### Create dummy coded variables

Given a variable x with n distinct values, create n new dummy coded variables coded 0/1 for presence (1) or absence (0) of each variable. A typical application would be to create dummy coded college majors from a vector of college majors. Can also combine categories by group. By default, NA values of x are returned as NA (added 10/20/17)

- Keywords
- multivariate, models

##### Usage

`dummy.code(x,group=NULL,na.rm=TRUE)`

##### Arguments

- x
A vector to be transformed into dummy codes

- group
A vector of categories to be coded as 1, all others coded as 0.

- na.rm
If TRUE, return NA for all codes with NA in x

##### Details

When coding demographic information, it is typical to create one variable with multiple categorical values (e.g., ethnicity, college major, occupation). `dummy.code`

will convert these categories into n distinct dummy coded variables.

If using dummy coded variables as predictors, remember to use n-1 variables.

If group is specified, then all values of x that are in group are given the value of 1, otherwise, 0. (Useful for combining a range of science majors into STEM or not. The example forms a dummy code of any smoking at all.)

##### Value

A matrix of dummy coded variables

##### Examples

```
# NOT RUN {
new <- dummy.code(sat.act$education)
new.sat <- data.frame(new,sat.act)
round(cor(new.sat,use="pairwise"),2)
dum.smoke <- dummy.code(spi$smoke,group=2:9)
table(dum.smoke,spi$smoke)
# }
```

*Documentation reproduced from package psych, version 1.8.12, License: GPL (>= 2)*