`prophet_reg()`

is a way to generate a *specification* of a PROPHET model
before fitting and allows the model to be created using
different packages. Currently the only package is `prophet`

.

## Usage

```
prophet_reg(
mode = "regression",
growth = NULL,
changepoint_num = NULL,
changepoint_range = NULL,
seasonality_yearly = NULL,
seasonality_weekly = NULL,
seasonality_daily = NULL,
season = NULL,
prior_scale_changepoints = NULL,
prior_scale_seasonality = NULL,
prior_scale_holidays = NULL,
logistic_cap = NULL,
logistic_floor = NULL
)
```

## Arguments

- mode
A single character string for the type of model. The only possible value for this model is "regression".

- growth
String 'linear' or 'logistic' to specify a linear or logistic trend.

- changepoint_num
Number of potential changepoints to include for modeling trend.

- changepoint_range
Adjusts the flexibility of the trend component by limiting to a percentage of data before the end of the time series. 0.80 means that a changepoint cannot exist after the first 80% of the data.

- seasonality_yearly
One of "auto", TRUE or FALSE. Toggles on/off a seasonal component that models year-over-year seasonality.

- seasonality_weekly
One of "auto", TRUE or FALSE. Toggles on/off a seasonal component that models week-over-week seasonality.

- seasonality_daily
One of "auto", TRUE or FALSE. Toggles on/off a seasonal componet that models day-over-day seasonality.

- season
'additive' (default) or 'multiplicative'.

- prior_scale_changepoints
Parameter modulating the flexibility of the automatic changepoint selection. Large values will allow many changepoints, small values will allow few changepoints.

- prior_scale_seasonality
Parameter modulating the strength of the seasonality model. Larger values allow the model to fit larger seasonal fluctuations, smaller values dampen the seasonality.

- prior_scale_holidays
Parameter modulating the strength of the holiday components model, unless overridden in the holidays input.

- logistic_cap
When growth is logistic, the upper-bound for "saturation".

- logistic_floor
When growth is logistic, the lower-bound for "saturation".

## Details

The data given to the function are not saved and are only used
to determine the *mode* of the model. For `prophet_reg()`

, the
mode will always be "regression".

The model can be created using the `fit()`

function using the
following *engines*:

"prophet" (default) - Connects to

`prophet::prophet()`

**Main Arguments**

The main arguments (tuning parameters) for the model are:

`growth`

: String 'linear' or 'logistic' to specify a linear or logistic trend.`changepoint_num`

: Number of potential changepoints to include for modeling trend.`changepoint_range`

: Range changepoints that adjusts how close to the end the last changepoint can be located.`season`

: 'additive' (default) or 'multiplicative'.`prior_scale_changepoints`

: Parameter modulating the flexibility of the automatic changepoint selection. Large values will allow many changepoints, small values will allow few changepoints.`prior_scale_seasonality`

: Parameter modulating the strength of the seasonality model. Larger values allow the model to fit larger seasonal fluctuations, smaller values dampen the seasonality.`prior_scale_holidays`

: Parameter modulating the strength of the holiday components model, unless overridden in the holidays input.`logistic_cap`

: When growth is logistic, the upper-bound for "saturation".`logistic_floor`

: When growth is logistic, the lower-bound for "saturation".

These arguments are converted to their specific names at the time that the model is fit.

Other options and argument can be
set using `set_engine()`

(See Engine Details below).

If parameters need to be modified, `update()`

can be used
in lieu of recreating the object from scratch.

## Engine Details

The standardized parameter names in `modeltime`

can be mapped to their original
names in each engine:

modeltime | prophet |

growth | growth ('linear') |

changepoint_num | n.changepoints (25) |

changepoint_range | changepoints.range (0.8) |

seasonality_yearly | yearly.seasonality ('auto') |

seasonality_weekly | weekly.seasonality ('auto') |

seasonality_daily | daily.seasonality ('auto') |

season | seasonality.mode ('additive') |

prior_scale_changepoints | changepoint.prior.scale (0.05) |

prior_scale_seasonality | seasonality.prior.scale (10) |

prior_scale_holidays | holidays.prior.scale (10) |

logistic_cap | df$cap (NULL) |

logistic_floor | df$floor (NULL) |

Other options can be set using `set_engine()`

.

**prophet**

The engine uses `prophet::prophet()`

.

Function Parameters:

```
#> function (df = NULL, growth = "linear", changepoints = NULL, n.changepoints = 25,
#> changepoint.range = 0.8, yearly.seasonality = "auto", weekly.seasonality = "auto",
#> daily.seasonality = "auto", holidays = NULL, seasonality.mode = "additive",
#> seasonality.prior.scale = 10, holidays.prior.scale = 10, changepoint.prior.scale = 0.05,
#> mcmc.samples = 0, interval.width = 0.8, uncertainty.samples = 1000,
#> fit = TRUE, ...)
```

Parameter Notes:

`df`

: This is supplied via the parsnip / modeltime`fit()`

interface (so don't provide this manually). See Fit Details (below).`holidays`

: A data.frame of holidays can be supplied via`set_engine()`

`uncertainty.samples`

: The default is set to 0 because the prophet uncertainty intervals are not used as part of the Modeltime Workflow. You can override this setting if you plan to use prophet's uncertainty tools.

Regressors:

Regressors are provided via the

`fit()`

or`recipes`

interface, which passes regressors to`prophet::add_regressor()`

Parameters can be controlled in

`set_engine()`

via:`regressors.prior.scale`

,`regressors.standardize`

, and`regressors.mode`

The regressor prior scale implementation default is

`regressors.prior.scale = 1e4`

, which deviates from the`prophet`

implementation (defaults to holidays.prior.scale)

Logistic Growth and Saturation Levels:

For

`growth = "logistic"`

, simply add numeric values for`logistic_cap`

and / or`logistic_floor`

. There is*no need*to add additional columns for "cap" and "floor" to your data frame.

Limitations:

`prophet::add_seasonality()`

is not currently implemented. It's used to specify non-standard seasonalities using fourier series. An alternative is to use`step_fourier()`

and supply custom seasonalities as Extra Regressors.

## Fit Details

**Date and Date-Time Variable**

It's a requirement to have a date or date-time variable as a predictor.
The `fit()`

interface accepts date and date-time features and handles them internally.

`fit(y ~ date)`

**Univariate (No Extra Regressors):**

For univariate analysis, you must include a date or date-time feature. Simply use:

Formula Interface (recommended):

`fit(y ~ date)`

will ignore xreg's.XY Interface:

`fit_xy(x = data[,"date"], y = data$y)`

will ignore xreg's.

**Multivariate (Extra Regressors)**

Extra Regressors parameter is populated using the `fit()`

or `fit_xy()`

function:

Only

`factor`

,`ordered factor`

, and`numeric`

data will be used as xregs.Date and Date-time variables are not used as xregs

`character`

data should be converted to factor.

*Xreg Example:* Suppose you have 3 features:

`y`

(target)`date`

(time stamp),`month.lbl`

(labeled month as a ordered factor).

The `month.lbl`

is an exogenous regressor that can be passed to the `arima_reg()`

using
`fit()`

:

`fit(y ~ date + month.lbl)`

will pass`month.lbl`

on as an exogenous regressor.`fit_xy(data[,c("date", "month.lbl")], y = data$y)`

will pass x, where x is a data frame containing`month.lbl`

and the`date`

feature. Only`month.lbl`

will be used as an exogenous regressor.

Note that date or date-time class values are excluded from `xreg`

.

## Examples

```
library(dplyr)
library(parsnip)
library(rsample)
library(timetk)
library(modeltime)
# Data
m750 <- m4_monthly %>% filter(id == "M750")
m750
#> # A tibble: 306 × 3
#> id date value
#> <fct> <date> <dbl>
#> 1 M750 1990-01-01 6370
#> 2 M750 1990-02-01 6430
#> 3 M750 1990-03-01 6520
#> 4 M750 1990-04-01 6580
#> 5 M750 1990-05-01 6620
#> 6 M750 1990-06-01 6690
#> 7 M750 1990-07-01 6000
#> 8 M750 1990-08-01 5450
#> 9 M750 1990-09-01 6480
#> 10 M750 1990-10-01 6820
#> # ℹ 296 more rows
# Split Data 80/20
splits <- initial_time_split(m750, prop = 0.8)
# ---- PROPHET ----
# Model Spec
model_spec <- prophet_reg() %>%
set_engine("prophet")
# Fit Spec
model_fit <- model_spec %>%
fit(log(value) ~ date, data = training(splits))
#> Disabling weekly seasonality. Run prophet with weekly.seasonality=TRUE to override this.
#> Disabling daily seasonality. Run prophet with daily.seasonality=TRUE to override this.
model_fit
#> parsnip model object
#>
#> PROPHET Model
#> - growth: 'linear'
#> - n.changepoints: 25
#> - changepoint.range: 0.8
#> - yearly.seasonality: 'auto'
#> - weekly.seasonality: 'auto'
#> - daily.seasonality: 'auto'
#> - seasonality.mode: 'additive'
#> - changepoint.prior.scale: 0.05
#> - seasonality.prior.scale: 10
#> - holidays.prior.scale: 10
#> - logistic_cap: NULL
#> - logistic_floor: NULL
#> - extra_regressors: 0
```