nullmodel: Fit a simple, non-informative model

Description Usage Arguments Details Value Examples

Description

Fit a single mean or largest class model. nullmodel() is the underlying computational function for the null_model() specification.

Usage

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nullmodel(x, ...)

## Default S3 method:
nullmodel(x = NULL, y, ...)

## S3 method for class 'nullmodel'
print(x, ...)

## S3 method for class 'nullmodel'
predict(object, new_data = NULL, type = NULL, ...)

Arguments

x

An optional matrix or data frame of predictors. These values are not used in the model fit

...

Optional arguments (not yet used)

y

A numeric vector (for regression) or factor (for classification) of outcomes

object

An object of class nullmodel

new_data

A matrix or data frame of predictors (only used to determine the number of predictions to return)

type

Either "raw" (for regression), "class" or "prob" (for classification)

Details

nullmodel() emulates other model building functions, but returns the simplest model possible given a training set: a single mean for numeric outcomes and the most prevalent class for factor outcomes. When class probabilities are requested, the percentage of the training set samples with the most prevalent class is returned.

Value

The output of nullmodel() is a list of class nullmodel with elements

call

the function call

value

the mean of y or the most prevalent class

levels

when y is a factor, a vector of levels. NULL otherwise

pct

when y is a factor, a data frame with a column for each class (NULL otherwise). The column for the most prevalent class has the proportion of the training samples with that class (the other columns are zero).

n

the number of elements in y

predict.nullmodel() returns a either a factor or numeric vector depending on the class of y. All predictions are always the same.

Examples

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outcome <- factor(sample(letters[1:2],
                         size = 100,
                         prob = c(.1, .9),
                         replace = TRUE))
useless <- nullmodel(y = outcome)
useless
predict(useless, matrix(NA, nrow = 5))

parsnip documentation built on July 8, 2020, 7:22 p.m.