parsnip: nullmodel – R documentation

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nullmodel

Fit a simple, non-informative model

Description

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

Usage

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 either a factor or numeric vector depending on the class of y. All predictions are always the same.

Examples

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

A Common API to Modeling and Analysis Functions

v0.1.5

GPL-2

Authors

Max Kuhn [aut, cre], Davis Vaughan [aut], RStudio [cph]

Initial release