# vl_regression

`vl_regression.Rd`

Add RegressionTransform to a vega-lite spec.

## Usage

```
vl_regression(
spec,
regression = NULL,
on = NULL,
as = NULL,
extent = NULL,
groupby = NULL,
method = NULL,
order = NULL,
params = NULL,
.object = NULL
)
```

## Arguments

- spec
An input vega-lite spec

- regression
The data field of the dependent variable to predict.

- on
The data field of the independent variable to use a predictor.

- as
The output field names for the smoothed points generated by the regression transform.

**Default value:**The field names of the input x and y values.- extent
A [min, max] domain over the independent (x) field for the starting and ending points of the generated trend line.

- groupby
The data fields to group by. If not specified, a single group containing all data objects will be used.

- method
The functional form of the regression model. One of

`"linear"`

,`"log"`

,`"exp"`

,`"pow"`

,`"quad"`

, or`"poly"`

.**Default value:**`"linear"`

- order
The polynomial order (number of coefficients) for the 'poly' method.

**Default value:**`3`

- params
A boolean flag indicating if the transform should return the regression model parameters (one object per group), rather than trend line points. The resulting objects include a

`coef`

array of fitted coefficient values (starting with the intercept term and then including terms of increasing order) and an`rSquared`

value (indicating the total variance explained by the model).**Default value:**`false`

- .object
Directly input an object, rather than creating one via the other arguments. Should not be used in conjunction with the other arguments other than

`spec`

. Objects can be of type: RegressionTransform