model.matrix.earth {earth} | R Documentation |

## Get the earth basis matrix

### Description

Get the basis matrix of an `earth`

model.

### Usage

```
## S3 method for class 'earth'
model.matrix(object = stop("no 'object' argument"),
x = NULL, subset = NULL, which.terms = NULL,
trace = 0,
...,
Env = parent.frame(),
Callers.name = "model.matrix.earth")
```

### Arguments

`object` |
An |

`x` |
Default is NULL, meaning use the original data
used to build the Else |

`subset` |
Which rows to use in |

`which.terms` |
Which terms to use.
Default is NULL, meaning all terms in the earth model
(i.e. the terms in |

`trace` |
Default 0. Set to non-zero to see which data |

`...` |
Unused, but provided for generic/method consistency. |

`Env` |
For internal use. |

`Callers.name` |
For internal use (used by earth in trace messages). |

### Value

A basis matrix `bx`

of the same form returned by `earth`

.
The format of `bx`

is described in `earth.object`

.

If `x`

, `subset`

, and `which.terms`

are all NULL (the
default), this function returns the model's `bx`

. In this case,
it is perhaps easier to simply use `object$bx`

.

The matrix `bx`

can be used
as the input matrix to `lm`

or `glm`

,
as shown below in the example.
In fact, that is what earth does internally after the pruning pass —
it calls `lm.fit`

,
and additionally `glm`

if earth's `glm`

argument is used.

### See Also

### Examples

```
# Example 1
data(trees)
earth.mod <- earth(Volume ~ ., data = trees) # standard earth model
summary(earth.mod, decomp = "none") # "none" to print terms in same order as lm.mod below
bx <- model.matrix(earth.mod) # earth model's basis mat (equivalent to bx <- earth.mod$bx)
lm.mod <- lm(trees$Volume ~ bx[,-1]) # -1 to drop intercept
summary(lm.mod) # yields same coeffs as above summary
# displayed t values are not meaningful
# Example 2
earth.mod <- earth(Volume~., data=trees) # standard earth model
summary(earth.mod, decomp = "none") # "none" to print terms in same order as lm.mod below
bx <- model.matrix(earth.mod) # earth model's basis mat (equivalent to bx <- earth.mod$bx)
bx <- bx[, -1] # drop intercept column
bx <- as.data.frame(bx) # lm requires a data frame
bx$Volume <- trees$Volume # add Volume to data
lm.mod <- lm(Volume~., data=bx) # standard linear regression on earth's basis mat
summary(lm.mod) # yields same coeffs as above summary
# displayed t values are not meaningful
```

*earth*version 5.3.3 Index]