# Developer helpers

Source:`R/estimator-helpers.R`

, `R/prob-helpers.R`

, `R/validation.R`

`developer-helpers.Rd`

Helpers to be used alongside `metric_vec_template()`

and
`metric_summarizer()`

when creating new metrics. See Custom performance metrics for more
information.

## Usage

```
get_weights(data, estimator)
finalize_estimator(x, estimator = NULL, metric_class = "default")
finalize_estimator_internal(metric_dispatcher, x, estimator)
dots_to_estimate(data, ...)
validate_estimator(estimator, estimator_override = NULL)
```

## Arguments

- data
A table with truth values as columns and predicted values as rows.

- estimator
Either

`NULL`

for auto-selection, or a single character for the type of estimator to use.- x
The column used to autoselect the estimator. This is generally the

`truth`

column, but can also be a table if your metric has table methods.- metric_class
A single character of the name of the metric to autoselect the estimator for. This should match the method name created for

`finalize_estimator_internal()`

.- metric_dispatcher
A simple dummy object with the class provided to

`metric_class`

. This is created and passed along for you.- ...
A set of unquoted column names or one or more

`dplyr`

selector functions to choose which variables contain the class probabilities. If`truth`

is binary, only 1 column should be selected. Otherwise, there should be as many columns as factor levels of`truth`

.- estimator_override
A character vector overriding the default allowed estimator list of

`c("binary", "macro", "micro", "macro_weighted")`

. Set this if your classification estimator does not support all of these methods.

## Weight Calculation

`get_weights()`

accepts a confusion matrix and an `estimator`

of type
`"macro"`

, `"micro"`

, or `"macro_weighted"`

and returns the correct weights.
It is useful when creating multiclass metrics.

## Estimator Selection

`finalize_estimator()`

is the engine for auto-selection of `estimator`

based
on the type of `x`

. Generally `x`

is the `truth`

column. This function
is called from the vector method of your metric.

`finalize_estimator_internal()`

is an S3 generic that you should extend for
your metric if it does not implement *only* the following estimator types:
`"binary"`

, `"macro"`

, `"micro"`

, and `"macro_weighted"`

.
If your metric does support all of these, the default version of
`finalize_estimator_internal()`

will autoselect `estimator`

appropriately.
If you need to create a method, it should take the form:
`finalize_estimator_internal.metric_name`

. Your method for
`finalize_estimator_internal()`

should do two things:

If

`estimator`

is`NULL`

, autoselect the`estimator`

based on the type of`x`

and return a single character for the`estimator`

.If

`estimator`

is not`NULL`

, validate that it is an allowed`estimator`

for your metric and return it.

If you are using the default for `finalize_estimator_internal()`

, the
`estimator`

is selected using the following heuristics:

If

`estimator`

is not`NULL`

, it is validated and returned immediately as no auto-selection is needed.If

`x`

is a:`factor`

- Then`"binary"`

is returned if it has 2 levels, otherwise`"macro"`

is returned.`numeric`

- Then`"binary"`

is returned.`table`

- Then`"binary"`

is returned if it has 2 columns, otherwise`"macro"`

is returned. This is useful if you have`table`

methods.`matrix`

- Then`"macro"`

is returned.

## Dots -> Estimate

`dots_to_estimate()`

is useful with class probability metrics that take
`...`

rather than `estimate`

as an argument. It constructs either a single
name if 1 input is provided to `...`

or it constructs a quosure where the
expression constructs a matrix of as many columns as are provided to `...`

.
These are eventually evaluated in the `summarise()`

call in
`metric_summarizer()`

and evaluate to either a vector or a matrix for further
use in the underlying vector functions.

## Estimator Validation

`validate_estimator()`

is called from your metric specific method of
`finalize_estimator_internal()`

and ensures that a user provided estimator
is of the right format and is one of the allowed values.