# MARS models via the `earth` package

Function | Works
--- | ---
`tidypredict_fit()`, `tidypredict_sql()`, `parse_model()` | ✔
`tidypredict_to_column()` | ✔
`tidypredict_test()` | ✔
`tidypredict_interval()`, `tidypredict_sql_interval()` | ✗
`parsnip` | ✔

## `tidypredict_` functions

    library(earth)
    data("etitanic", package = "earth")

    model <- earth(age ~ sibsp + parch, data = etitanic, degree = 3)

- Create the R formula

      tidypredict_fit(model)
      #> 22.2918960405404 + (ifelse(parch < 2, 2 - parch, 0) * 4.85356462114356) +
      #>     (ifelse(parch > 2, parch - 2, 0) * 13.0493891423279) + (ifelse(parch >
      #>     4, parch - 4, 0) * -18.8998708031825) + (ifelse(sibsp > 1,
      #>     sibsp - 1, 0) * -7.71566779782014) + (ifelse(sibsp > 1, sibsp -
      #>     1, 0) * ifelse(parch < 1, 1 - parch, 0) * 7.40395975552271) +
      #>     (ifelse(sibsp > 1, sibsp - 1, 0) * ifelse(parch > 1, parch -
      #>         1, 0) * 4.41874354843213)

- SQL output example

      tidypredict_sql(model, dbplyr::simulate_odbc())
      #> <SQL> (((((22.2918960405404 + (CASE WHEN (`parch` < 2.0) THEN (2.0 - `parch`) WHEN NOT (`parch` < 2.0) THEN 0.0 END * 4.85356462114356)) + (CASE WHEN (`parch` > 2.0) THEN (`parch` - 2.0) WHEN NOT (`parch` > 2.0) THEN 0.0 END * 13.0493891423279)) + (CASE WHEN (`parch` > 4.0) THEN (`parch` - 4.0) WHEN NOT (`parch` > 4.0) THEN 0.0 END * -18.8998708031825)) + (CASE WHEN (`sibsp` > 1.0) THEN (`sibsp` - 1.0) WHEN NOT (`sibsp` > 1.0) THEN 0.0 END * -7.71566779782014)) + ((CASE WHEN (`sibsp` > 1.0) THEN (`sibsp` - 1.0) WHEN NOT (`sibsp` > 1.0) THEN 0.0 END * CASE WHEN (`parch` < 1.0) THEN (1.0 - `parch`) WHEN NOT (`parch` < 1.0) THEN 0.0 END) * 7.40395975552271)) + ((CASE WHEN (`sibsp` > 1.0) THEN (`sibsp` - 1.0) WHEN NOT (`sibsp` > 1.0) THEN 0.0 END * CASE WHEN (`parch` > 1.0) THEN (`parch` - 1.0) WHEN NOT (`parch` > 1.0) THEN 0.0 END) * 4.41874354843213)

- Add the prediction to the original table

      library(dplyr)

      etitanic %>%
        tidypredict_to_column(model) %>%
        glimpse()
      #> Rows: 1,046
      #> Columns: 7
      #> $ pclass   <fct> 1st, 1st, 1st, 1st, 1st, 1st, 1st, 1st, 1st, 1st, 1st, 1st, 1…
      #> $ survived <int> 1, 1, 0, 0, 0, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1, 0, 1, 1, 0, 1, 1…
      #> $ sex      <fct> female, male, female, male, female, male, female, male, femal…
      #> $ age      <dbl> 29.0000, 0.9167, 2.0000, 30.0000, 25.0000, 48.0000, 63.0000, …
      #> $ sibsp    <int> 0, 1, 1, 1, 1, 0, 1, 0, 2, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 1…
      #> $ parch    <int> 0, 2, 2, 2, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1…
      #> $ fit      <dbl> 31.99903, 22.29190, 22.29190, 22.29190, 22.29190, 31.99903, 3…

- Confirm that `tidypredict` results match to the model’s `predict()` results

      tidypredict_test(model, etitanic)
      #> tidypredict test results
      #> Difference threshold: 1e-12
      #>
      #>  All results are within the difference threshold

## GLM models

`tidypredict` supports the `glm` argument as well:

    model <- earth(survived ~ .,
      data = etitanic,
      glm = list(family = binomial), degree = 2
    )

    tidypredict_fit(model)
    #> 1 - 1/(1 + exp(2.91352600741338 + (ifelse(age > 32, age - 32,
    #>     0) * -0.0375714917713112) + (ifelse(pclass == "2nd", 1, 0) *
    #>     ifelse(sex == "male", 1, 0) * -1.76809447811121) + (ifelse(pclass ==
    #>     "3rd", 1, 0) * -5.03005595780699) + (ifelse(pclass == "3rd",
    #>     1, 0) * ifelse(sibsp < 4, 4 - sibsp, 0) * 0.618652747659854) +
    #>     (ifelse(pclass == "3rd", 1, 0) * ifelse(sex == "male", 1,
    #>         0) * 1.22269536265148) + (ifelse(sex == "male", 1, 0) *
    #>     -3.18562450248533) + (ifelse(sex == "male", 1, 0) * ifelse(age <
    #>     16, 16 - age, 0) * 0.241814028713259)))

The spec sets the `is_glm` entry to 1, as well as the `family` and `link` entries.

    str(parse_model(model), 2)
    #> List of 2
    #>  $ general:List of 6
    #>   ..$ model  : chr "earth"
    #>   ..$ type   : chr "regression"
    #>   ..$ version: num 2
    #>   ..$ is_glm : num 1
    #>   ..$ family : chr "binomial"
    #>   ..$ link   : chr "logit"
    #>  $ terms  :List of 8
    #>   ..$ :List of 4
    #>   ..$ :List of 4
    #>   ..$ :List of 4
    #>   ..$ :List of 4
    #>   ..$ :List of 4
    #>   ..$ :List of 4
    #>   ..$ :List of 4
    #>   ..$ :List of 4
    #>  - attr(*, "class")= chr [1:3] "parsed_model" "pm_regression" "list"

## parsnip

`parsnip` fitted models are also supported by `tidypredict`:

    library(parsnip)

    p_model <- mars(mode = "regression", prod_degree = 3) %>%
      set_engine("earth") %>%
      fit(age ~ sibsp + parch, data = etitanic)

    tidypredict_fit(p_model)
    #> 22.2918960405404 + (ifelse(parch < 2, 2 - parch, 0) * 4.85356462114356) +
    #>     (ifelse(parch > 2, parch - 2, 0) * 13.0493891423279) + (ifelse(parch >
    #>     4, parch - 4, 0) * -18.8998708031825) + (ifelse(sibsp > 1,
    #>     sibsp - 1, 0) * -7.71566779782014) + (ifelse(sibsp > 1, sibsp -
    #>     1, 0) * ifelse(parch < 1, 1 - parch, 0) * 7.40395975552271) +
    #>     (ifelse(sibsp > 1, sibsp - 1, 0) * ifelse(parch > 1, parch -
    #>         1, 0) * 4.41874354843213)

## Parse model spec

Here is an example of the model spec:

    pm <- parse_model(model)
    str(pm, 2)
    #> List of 2
    #>  $ general:List of 6
    #>   ..$ model  : chr "earth"
    #>   ..$ type   : chr "regression"
    #>   ..$ version: num 2
    #>   ..$ is_glm : num 1
    #>   ..$ family : chr "binomial"
    #>   ..$ link   : chr "logit"
    #>  $ terms  :List of 8
    #>   ..$ :List of 4
    #>   ..$ :List of 4
    #>   ..$ :List of 4
    #>   ..$ :List of 4
    #>   ..$ :List of 4
    #>   ..$ :List of 4
    #>   ..$ :List of 4
    #>   ..$ :List of 4
    #>  - attr(*, "class")= chr [1:3] "parsed_model" "pm_regression" "list"

    str(pm$terms[1:2])
    #> List of 2
    #>  $ :List of 4
    #>   ..$ label       : chr "(Intercept)"
    #>   ..$ coef        : num 2.91
    #>   ..$ is_intercept: num 1
    #>   ..$ fields      :List of 1
    #>   .. ..$ : list()
    #>  $ :List of 4
    #>   ..$ label       : chr "h(age-32)"
    #>   ..$ coef        : num -0.0376
    #>   ..$ is_intercept: num 0
    #>   ..$ fields      :List of 1
    #>   .. ..$ :List of 4
    #>   .. .. ..$ type: chr "operation"
    #>   .. .. ..$ col : chr "age"
    #>   .. .. ..$ val : num 32
    #>   .. .. ..$ op  : chr "morethan"