`embed`

is a package that contains extra steps for the `recipes`

package for embedding predictors into one or more numeric columns. All of the preprocessing methods are *supervised*.

These steps are contained in a separate package because the package dependencies, `rstanarm`

, `lme4`

, and `keras`

, are fairly heavy.

The steps for categorical predictors are:

`step_lencode_glm()`

,`step_lencode_bayes()`

, and`step_lencode_mixed()`

estimate the effect of each of the factor levels on the outcome and these estimates are used as the new encoding. The estimates are estimated by a generalized linear model. This step can be executed without pooling (via`glm`

) or with partial pooling (`stan_glm`

or`lmer`

). Currently implemented for numeric and two-class outcomes.`step_embed()`

uses`keras::layer_embedding`

to translate the original*C*factor levels into a set of*D*new variables (<*C*). The model fitting routine optimizes which factor levels are mapped to each of the new variables as well as the corresponding regression coefficients (i.e., neural network weights) that will be used as the new encodings.`step_woe()`

creates new variables based on weight of evidence encodings.`step_feature_hash()`

can create indicator variables using feature hashing.

For numeric predictors:

`step_umap()`

uses a nonlinear transformation similar to t-SNE but can be used to project the transformation on new data. Both supervised and unsupervised methods can be used.`step_discretize_xgb()`

and`step_discretize_cart()`

can make binned versions of numeric predictors using supervised tree-based models.

Some references for these methods are:

- Francois C and Allaire JJ (2018)
*Deep Learning with R*, Manning - Guo, C and Berkhahn F (2016) “Entity Embeddings of Categorical Variables”
- Micci-Barreca D (2001) “A preprocessing scheme for high-cardinality categorical attributes in classification and prediction problems,” ACM SIGKDD Explorations Newsletter, 3(1), 27-32.
- Zumel N and Mount J (2017) “
`vtreat`

: a`data.frame`

Processor for Predictive Modeling” - McInnes L and Healy J (2018) UMAP: Uniform Manifold Approximation and Projection for Dimension Reduction
- Good, I. J. (1985), “Weight of evidence: A brief survey”, Bayesian Statistics, 2, pp.249-270.

There are two articles that walk through how to use these embedding steps, using generalized linear models and neural networks built via TensorFlow.

To install the package:

`install.packages("embed")`

Note that, to use some steps, you will also have to load other packages such as `rstanarm`

and `lme4`

. For all of the steps to work, you may want to use:

`install.packages(c("rpart", "xgboost", "rstanarm", "lme4"))`

To get a bug fix or to use a feature from the development version, you can install the development version of this package from GitHub.

```
# install.packages("remotes")
remotes::install_github("tidymodels/embed")
```

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