mars.to.earth {earth} | R Documentation |
Convert a ‘mars’ object to an ‘earth’ object
mars.to.earth(object)
object |
A ‘mars’ object, created using mars in the mda package.
|
The value is the same format as that returned by earth
but
with skeletal versions of rss.per.subset
, gcv.per.subset
, and prune.terms
.
You can fully initialise these components by calling update.earth
after mars.to.earth
, but if you do this selected.terms
may change.
However with pmethod="backward"
a change is unlikely —
selected.terms
would change only if GCVs are so close that numerical errors
have an effect.
Perhaps the most notable difference between
earth and mars objects is that mars
returns the
MARS basis matrix in a field called "x
"
whereas earth
returns "bx
" with only the selected terms.
Also, earth
returns "dirs
" rather than "factors
",
and in earth
this matrix can have entries of value 2 for linear predictors.
For details of other differences between earth and mars objects,
see the comments in the source code of mars.to.earth()
.
## Not run: # The example is not run with example("mars.to.earth") because that would # require making the earth package dependent on the mda package. library(mda) a <- mars(trees[,-3], trees[,3]) a <- mars.to.earth(a) summary(a, digits = 2) # the standard earth functions can now be used # yields (note the reconstructed call): # Call: # earth(x = trees[, -3], y = trees[, 3]) # # Expression: # 20 # + 5.4 * pmax(0, Girth - 12) # - 2.6 * pmax(0, 12 - Girth) # + 0.72 * pmax(0, Height - 76) # # Number of cases: 31 # Selected 4 of 5 terms, and 2 of 2 predictors # Number of terms at each degree of interaction: 1 3 (additive model) # GCV: 13 RSS: 251 GRSq: 0.95 RSq: 0.97 ## End(Not run)