Dummy {DescTools} | R Documentation |

## Generate Dummy Codes for a Factor

### Description

Generate a matrix of dummy codes (class indicators) for a given factor.

### Usage

```
Dummy(x, method = c("treatment", "sum", "helmert", "poly", "full"),
base = 1, levels = NULL)
```

### Arguments

`x` |
factor or vector of classes for cases. |

`method` |
defines the method of the contrasts being formed. Can be one
out of |

`base` |
an integer specifying which group is considered the baseline group. |

`levels` |
an optional vector of the values (as character strings) that |

### Details

For reverting dummy codes see the approach in the examples below.

### Value

a matrix with the dummy codes.
The number of rows correspond to the number of elements in `x`

and the number of columns to the number of its levels - 1, respectively to the number of levels given as argument -1.

When `method = "full"`

is chosen the number of columns will correspond to the number of levels.

### Author(s)

Andri Signorell <andri@signorell.net>

### References

Venables, W N and Ripley, B D (2002): *Modern Applied Statistics with S*. Fourth edition. Springer.

### See Also

`model.frame`

, `contrasts`

, `class.ind`

in the package nnet

### Examples

```
x <- c("red","blue","green","blue","green","red","red","blue")
Dummy(x)
Dummy(x, base=2)
Dummy(x, method="sum")
y <- c("Max","Max","Max","Max","Max","Bill","Bill","Bill")
Dummy(y)
Dummy(y, base="Max")
Dummy(y, base="Max", method="full")
# "Undummy" (revert the dummy coding)
m <- Dummy(y, method="full")
m
z <- apply(m, 1, function(x) colnames(m)[x==1])
z
identical(y, as.vector(z))
m <- Dummy(y)
m
z <- apply(m, 1, function(x) ifelse(sum(x)==0, attr(m,"base"), colnames(m)[x==1]))
z
```

*DescTools*version 0.99.54 Index]