stats::glm() fits a generalized linear model for numeric outcomes. A linear combination of the predictors is used to model the numeric outcome via a link function.

## Details

For this engine, there is a single mode: regression

### Tuning Parameters

This engine has no tuning parameters but you can set the family parameter (and/or link) as an engine argument (see below).

### Translation from parsnip to the original package

linear_reg() %>%
set_engine("glm") %>%
translate()

## Linear Regression Model Specification (regression)
##
## Computational engine: glm
##
## Model fit template:
## stats::glm(formula = missing_arg(), data = missing_arg(), weights = missing_arg(),
##     family = stats::gaussian)

To use a non-default family and/or link, pass in as an argument to set_engine():

linear_reg() %>%
set_engine("glm", family = stats::poisson(link = "sqrt")) %>%
translate()

## Linear Regression Model Specification (regression)
##
## Engine-Specific Arguments:
##   family = stats::poisson(link = "sqrt")
##
## Computational engine: glm
##
## Model fit template:
## stats::glm(formula = missing_arg(), data = missing_arg(), weights = missing_arg(),
##     family = stats::poisson(link = "sqrt"))

### Preprocessing requirements

Factor/categorical predictors need to be converted to numeric values (e.g., dummy or indicator variables) for this engine. When using the formula method via fit(), parsnip will convert factor columns to indicators.

### Case weights

This model can utilize case weights during model fitting. To use them, see the documentation in case_weights and the examples on tidymodels.org.

The fit() and fit_xy() arguments have arguments called case_weights that expect vectors of case weights.

However, the documentation in stats::glm() assumes that is specific type of case weights are being used:“Non-NULL weights can be used to indicate that different observations have different dispersions (with the values in weights being inversely proportional to the dispersions); or equivalently, when the elements of weights are positive integers w_i, that each response y_i is the mean of w_i unit-weight observations. For a binomial GLM prior weights are used to give the number of trials when the response is the proportion of successes: they would rarely be used for a Poisson GLM.”

### Saving fitted model objects

This model object contains data that are not required to make predictions. When saving the model for the purpose of prediction, the size of the saved object might be substantially reduced by using functions from the butcher package.

### Examples

The “Fitting and Predicting with parsnip” article contains examples for linear_reg() with the "glm" engine.

### References

• Kuhn, M, and K Johnson. 2013. Applied Predictive Modeling. Springer.