# Driverless AI Transformations¶

Transformations in Driverless AI are applied to columns in the data. The transformers create the engineered features in experiments.

Driverless AI provides a number of transformers. The downloaded experiment logs include the transformations that were applied to your experiment. Note that you can exclude transformations in the **config.toml** file, and that list of excluded transformers will also be available in the experiment log.

## Available Transformers¶

The following transformers are available for classification (multiclass and binary) and regression experiments.

### Numeric Transformers (Integer, Real, Binary)¶

BulkInteractionsTransformer

The Bulk Interactions Transformer add, divide, multiply, and subtract two numeric columns in the data to create a new feature.

ClusterDistTransformer

The Cluster Distance Transformer clusters selected numeric columns and uses the distance to a specific cluster as a new feature.

ClusterTETransformer

The Cluster Target Encoding Transformer clusters selected numeric columns and calculates the mean of the response column for each cluster. The mean of the response is used as a new feature. Cross Validation is used to calculate mean response to prevent overfitting.

NumCatTETransformer

The Numeric Categorical Target Encoding Transformer calculates the mean of the response column for several selected columns. If one of the selected columns is numeric, it is first converted to categorical by binning. The mean of the response column is used as a new feature. Cross Validation is used to calculate mean response to prevent overfitting.

NumToCatTETransformer

The Numeric to Categorical Target Encoding Transformer converts numeric columns to categoricals by binning and then calculates the mean of the response column for each group. The mean of the response for the bin is used as a new feature. Cross Validation is used to calculate mean response to prevent overfitting.

NumToCatWoEMonotonicTransformer

The Numeric to Categorical Weight of Evidence Monotonic Transformer converts a numeric column to categorical by binning and then calculates Weight of Evidence for each bin. The monotonic constraint ensures the bins of values are monotonically related to the Weight of Evidence value. The Weight of Evidence is used as a new feature. Weight of Evidence measures the “strength” of a grouping for separating good and bad risk and is calculated by taking the log of the ratio of distributions for a binary response column.

NumToCatWoETransformer

The Numeric to Categorical Weight of Evidence Transformer converts a numeric column to categorical by binning and then calculates Weight of Evidence for each bin. The Weight of Evidence is used as a new feature. Weight of Evidence measures the “strength” of a grouping for separating good and bad risk and is calculated by taking the log of the ratio of distributions for a binary response column.

TruncSVDNumTransformer

Truncated SVD Transformer trains a Truncated SVD model on selected numeric columns and uses the components of the truncated SVD matrix as new features.

### Time Series Experiments Transformers¶

LagsTransformer

The Lags Transformer creates target/feature lags, possibly over groups. Each lag is used as a new feature. Lag transformers may apply to categorical (strings) features or binary/multiclass string valued targets after they have been internally numerically encoded.

LagsAggregatesTransformer

The Lags Aggregates Transformer calculates aggregations of target/feature lags like mean(lag7, lag14, lag21) with support for mean, min, max, median, sum, skew, kurtosis, std. The aggregation is used as a new feature.

EwmaLagsTransformer

The Exponentially Weighted Moving Average (EWMA) Transformer calculates the exponentially weighted moving average of target or feature lags.

LagsInteractionTransformer

The Lags Interaction Transformer creates target/feature lags and calculates interactions between the lags (lag2 - lag1, for instance). The interaction is used as a new feature.

### Categorical Transformers (String)¶

CVCatNumEncode

The Cross Validationcal Categorical to Numeric Encoding Transformer calculates an aggregation of a numeric column for each value in a categorical column (ex: calculate the mean Temperature for each City) and uses this aggregation as a new feature.

CVTargetEncode

The Cross Validation Target Encoding Transformer calculates the mean of the response column for each value in a categorical column and uses this as a new feature. Cross Validation is used to calculate mean response to prevent overfitting.

FrequentTransformer

The Frequent Transformer calculates the frequency for each value in categorical column(s) and uses this as a new feature. This count can be either the raw count or the normalized count.

LexiLabelEncoder

The Lexi Label Encoder sorts a categorical column in lexigraphical order and uses the order index created as a new feature.

NumCatTETransformer

The Numeric Categorical Target Encoding Transformer calculates the mean of the response column for several selected columns. If one of the selected columns is numeric, it is first converted to categorical by binning. The mean of the response column is used as a new feature. Cross Validation is used to calculate mean response to prevent overfitting.

OHETransformer

The One-hot Encoding transformer converts a categorical column to a series of boolean features by performing one-hot encoding. The boolean features are used as new features.

SortedLETransformer

The Sorted Label Encoding Transformer sorts a categorical column by the response column and uses the order index created as a new feature.

WeightOfEvidenceTransformer

The Weight of Evidence Transformer calculates Weight of Evidence for each value in categorical column(s). The Weight of Evidence is used as a new feature. Weight of Evidence measures the “strength” of a grouping for separating good and bad risk and is calculated by taking the log of the ratio of distributions for a binary response column.

This only works with a binary target variable. The likelihood needs to be created within a stratified kfold if a fit_transform method is used. More information can be found here: http://ucanalytics.com/blogs/information-value-and-weight-of-evidencebanking-case/.

### Text Transformers (String)¶

TextBiGRUTransformer

Trains a bi-directional GRU Tensorflow model on word embeddings created from a text feature to predict the response column. The GRU prediction is used as a new a feature. Cross Validation is used when training the GRU model to prevent overfitting.

TextCharCNNTransformer

Trains a CNN Tensorflow model on character embeddings created from a text feature to predict the response column. The CNN prediction is used as a new a feature. Cross Validation is used when training the CNN model to prevent overfitting.

TextClustDistTransformer

The Text Cluster Distance Transformer clusters a TF-IDF matrix created from a text feature and uses the distance to a specific cluster as a new feature.

TextClustTETransformer

The Text Cluster Target Encoding Transformer clusters a TF-IDF matrix created from a text feature. The mean of the response is calculated for each cluster and this is used as a new feature. Cross Validation is used to calculate mean response to prevent overfitting.

TextCNNTransformer

The Text CNN Transformer trains a CNN Tensorflow model on word embeddings created from a text feature to predict the response column. The CNN prediction is used as a new a feature. Cross Validation is used when training the CNN model to prevent overfitting.

TextLinModelTransformer

The Text Linear Model Transformer trains a linear model on a TF-IDF matrix created from a text feature to predict the response column. The linear model prediction is used as a new feature. Cross Validation is used when training the linear model to prevent overfitting.

TextTransformer

The Text Transformer tokenizes a text column and creates a TFIDF matrix (term frequency-inverse document frequency) or count (count of the word) matrix. This may be followed by dimensionality reduction using truncated SVD. Selected components of the TF-IDF/Count matrix are used as new features.

### Time Transformers (Date, Time)¶

DatesTransformer

The Dates Transformer retrieves any date values, including:

- Year
- Quarter
- Month
- Day
- Day of year
- Week
- Week day
- Hour
- Minute
- Second

IsHolidayTransformer

The Is Holiday Transformer determines if a date column is a holiday. A boolean column indicating if the date is a holiday is added as a new feature. Creates a separate feature for holidays in the United States, United Kingdom, Germany, Mexico, and the European Central Bank. Other countries available in the python Holiday package can be added via the configuration file.

## Example Transformations¶

In this section, we will describe some of the available transformations using the example of predicting house prices on the example dataset.

Date Built | Square Footage | Num Beds | Num Baths | State | Price |
---|---|---|---|---|---|

01/01/1920 | 1700 | 3 | 2 | NY | $700K |

### Frequent Transformer¶

- the count of each categorical value in the dataset
- the count can be either the raw count or the normalized count

Date Built | Square Footage | Num Beds | Num Baths | State | Price | Freq_State |
---|---|---|---|---|---|---|

01/01/1920 | 1700 | 3 | 2 | NY | 700,000 | 4,500 |

There are 4,500 properties in this dataset with state = NY.

### Bulk Interactions Transformer¶

- add, divide, multiply, and subtract two columns in the data

Date Built | Square Footage | Num Beds | Num Baths | State | Price | Interaction_NumBeds#subtract#NumBaths |
---|---|---|---|---|---|---|

01/01/1920 | 1700 | 3 | 2 | NY | 700,000 | 1 |

There is one more bedroom than there are number of bathrooms for this property.

### Truncated SVD Numeric Transformer¶

- truncated SVD trained on selected numeric columns of the data
- the components of the truncated SVD will be new features

Date Built | Square Footage | Num Beds | Num Baths | State | Price | TruncSVD_Price_NumBeds_NumBaths_1 |
---|---|---|---|---|---|---|

01/01/1920 | 1700 | 3 | 2 | NY | 700,000 | 0.632 |

The first component of the truncated SVD of the columns Price, Number of Beds, Number of Baths.

### Dates Transformer¶

- get year, get quarter, get month, get day, get day of year, get week, get week day, get hour, get minute, get second

Date Built | Square Footage | Num Beds | Num Baths | State | Price | DateBuilt_Month |
---|---|---|---|---|---|---|

01/01/1920 | 1700 | 3 | 2 | NY | 700,000 | 1 |

The home was built in the month January.

### Text Transformer¶

- transform text column using methods: TFIDF or count (count of the word)
- this may be followed by dimensionality reduction using truncated SVD

### Categorical Target Encoding Transformer¶

- cross validation target encoding done on a categorical column

Date Built | Square Footage | Num Beds | Num Baths | State | Price | CV_TE_State |
---|---|---|---|---|---|---|

01/01/1920 | 1700 | 3 | 2 | NY | 700,000 | 550,000 |

The average price of properties in NY state is $550,000*.

*In order to prevent overfitting, Driverless AI calculates this average on out-of-fold data using cross validation.

### Numeric to Categorical Target Encoding Transformer¶

- numeric column converted to categorical by binning
- cross validation target encoding done on the binned numeric column

Date Built | Square Footage | Num Beds | Num Baths | State | Price | CV_TE_SquareFootage |
---|---|---|---|---|---|---|

01/01/1920 | 1700 | 3 | 2 | NY | 700,000 | 345,000 |

The column `Square Footage`

has been bucketed into 10 equally populated bins. This property lies in the `Square Footage`

bucket 1,572 to 1,749. The average price of properties with this range of square footage is $345,000*.

*In order to prevent overfitting, Driverless AI calculates this average on out-of-fold data using cross validation.

### Cluster Target Encoding Transformer¶

- selected columns in the data are clustered
- target encoding is done on the cluster ID

Date Built | Square Footage | Num Beds | Num Baths | State | Price | ClusterTE_4_NumBeds_NumBaths_SquareFootage |
---|---|---|---|---|---|---|

01/01/1920 | 1700 | 3 | 2 | NY | 700,000 | 450,000 |

The columns: `Num Beds`

, `Num Baths`

, `Square Footage`

have been segmented into 4 clusters. The average price of properties in the same cluster as the selected property is $450,000*.

*In order to prevent overfitting, Driverless AI calculates this average on out-of-fold data using cross validation.

### Cluster Distance Transformer¶

- selected columns in the data are clustered
- the distance to a chosen cluster center is calculated

Date Built | Square Footage | Num Beds | Num Baths | State | Price | ClusterDist_4_NumBeds_NumBaths_SquareFootage_1 |
---|---|---|---|---|---|---|

01/01/1920 | 1700 | 3 | 2 | NY | 700,000 | 0.83 |

The columns: `Num Beds`

, `Num Baths`

, `Square Footage`

have been segmented into 4 clusters. The difference from this record to Cluster 1 is 0.83.