earth: format.earth – R documentation

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format.earth

Format earth objects

Description

Return a string representing an earth expression (summary.earth calls this function internally to display the terms of the earth model).

Usage

## S3 method for class 'earth'
format(x = stop("no 'x' argument"),
       style = "h", decomp = "anova", digits = getOption("digits"),
       use.names = TRUE, colon.char = ":", ...)

Arguments

`x`	An `earth` object. This is the only required argument.
`style`	Formatting style. One of `"h"` (default) more compact `"pmax"` for those who prefer it `"max"` is the same as `"pmax"` but prints `max` rather than `pmax` `"C"` C style expression with zero based indexing `"bf"` basis function format
`decomp`	One of `"anova"` (default) order the terms using the "anova decomposition", i.e., in increasing order of interaction `"none"` order the terms as created during the earth forward pass.
`digits`	Number of significant digits. The default is `getOption(digits)`.
`use.names`	One of `TRUE` (default), use variable names if available. `FALSE` use names of the form `x[,1]`.
`colon.char`	Change colons in the returned string to colon.char. Default is ":" (no change). Specifying `colon.char=""` can be useful in some contexts to change names of the form `x1:x2` to `x1x2`.
`...`	Unused, but provided for generic/method consistency.

Value

A character representation of the earth model.

If there are multiple responses, format.earth will return multiple strings.

If there are embedded GLM model(s), the strings for the GLM model(s) come after the strings for the standard earth model(s).

Note

The FAQ section in the package vignette gives precise details of the "anova" ordering.

Using format.earth, perhaps after hand editing the returned string, you can create an alternative to predict.earth. For example:

as.func <- function(object, digits = 8, use.names = FALSE, ...)
  eval(parse(text=paste(
    "function(x){\n",
    "if(is.vector(x))\n",
    "  x <- matrix(x, nrow = 1, ncol = length(x))\n",
    "with(as.data.frame(x),\n",
    format(object, digits = digits, use.names = use.names, style = "pmax", ...),
    ")\n",
    "}\n", sep = "")))

earth.mod <- earth(Volume ~ ., data = trees)
my.func <- as.func(earth.mod, use.names = FALSE)
my.func(c(10,80))             # returns 16.84
predict(earth.mod, c(10,80))  # returns 16.84

Note that with pmax the R expression generated by format.earth can handle multiple cases. Thus the expression is consistent with the way predict functions usually work in R — we can give predict multiple cases (i.e., multiple rows in the input matrix) and it will return a vector of predicted values.

The earth package also provides a function format.lm. It has arguments as follows
format.lm(x, digits=getOption("digits"), use.names=TRUE, colon.char=":")
(Strictly speaking, format.lm doesn't belong in the earth package.) Example:

lm.mod <- lm(Volume ~ Height*Girth, data = trees)
cat(format(lm.mod, colon.char="*"))

# yields:
#    69.4
#    -  1.30 * Height
#    -  5.86 * Girth
#    + 0.135 * Height*Girth

Examples

earth.mod <- earth(Volume ~ ., data = trees)
cat(format(earth.mod))

# yields:
#    37.9
#    -  3.92 * h(16-Girth)
#    +   7.4 * h(Girth-16)
#    + 0.484 * h(Height-75)

cat(format(earth.mod, style="pmax"))

# yields:
#    37.9
#    -  3.92 * pmax(0,     16 -  Girth)
#    +   7.4 * pmax(0,  Girth -     16)
#    + 0.484 * pmax(0, Height -     75)

cat(format(earth.mod, style="C"))

# yields (note zero based indexing):
#  37.927
#    -  3.9187 * max(0,   16 - x[0])
#    +  7.4011 * max(0, x[0] -   16)
#    + 0.48411 * max(0, x[1] -   75)

cat(format(earth.mod, style="bf"))

# yields:
#    37.9
#    -  3.92 * bf1
#    +   7.4 * bf2
#    + 0.484 * bf3
#
#     bf1  h(16-Girth)
#     bf2  h(Girth-16)
#     bf3  h(Height-75)

earth

Multivariate Adaptive Regression Splines

v5.3.0

GPL-3

Authors

Stephen Milborrow. Derived from mda:mars by Trevor Hastie and Rob Tibshirani. Uses Alan Miller's Fortran utilities with Thomas Lumley's leaps wrapper.

Initial release