*seasonal* is an easy-to-use and full-featured R-interface to X-13ARIMA-SEATS, the newest seasonal adjustment software developed by the United States Census Bureau.

*seasonal* depends on the x13binary package to access pre-built binaries of X-13ARIMA-SEATS on all platforms and does not require any manual installation. To install both packages:

`install.packages("seasonal")`

`seas`

is the core function of the *seasonal* package. By default, `seas`

calls the automatic procedures of X-13ARIMA-SEATS to perform a seasonal adjustment that works well in most circumstances:

`m <- seas(AirPassengers)`

For a more detailed introduction, check our article in the *Journal of Statistical Software* or consider the vignette:

`vignette("seas")`

In *seasonal*, it is possible to use almost the complete syntax of X-13ARIMA-SEATS. The X-13ARIMA-SEATS syntax uses *specs* and *arguments*, with each spec optionally containing some arguments. These spec-argument combinations can be added to `seas`

by separating the spec and the argument by a dot (`.`

). For example, in order to set the ‘variables’ argument of the ‘regression’ spec equal to `td`

and `ao1999.jan`

, the input to `seas`

looks like this:

`m <- seas(AirPassengers, regression.variables = c("td", "ao1955.jan"))`

The best way to learn about the relationship between the syntax of X-13ARIMA-SEATS and *seasonal* is to study the comprehensive list of examples. Detailed information on the options can be found in the Census Bureaus’ official manual.

*seasonal* has a flexible mechanism to read data from X-13ARIMA-SEATS. With the `series`

function, it is possible to import almost all output that can be generated by X-13ARIMA-SEATS. For example, the following command returns the forecasts of the ARIMA model as a `"ts"`

time series:

```
m <- seas(AirPassengers)
series(m, "forecast.forecasts")
```

There are several graphical tools to analyze a `seas`

model. The main plot function draws the seasonally adjusted and unadjusted series, as well as the outliers:

```
m <- seas(AirPassengers, regression.aictest = c("td", "easter"))
plot(m)
```

The `view`

function is a graphical tool for choosing a seasonal adjustment model, using the seasonalview package, with the same structure as the demo website of seasonal. To install seasonalview, type:

`install.packages("seasonalview")`

The goal of `view`

is to summarize all relevant options, plots and statistics that should be usually considered. `view`

uses a `"seas"`

object as its main argument:

`view(m)`

*seasonal* is free and open source, licensed under GPL-3. It requires the X-13ARIMA-SEATS software by the U.S. Census Bureau, which is open source and freely available under the terms of its own license.

To cite seasonal in publications use:

Sax C, Eddelbuettel D (2018). “Seasonal Adjustment by X-13ARIMA-SEATS in R.” *Journal of Statistical Software*, *87*(11), 1-17. doi: 10.18637/jss.v087.i11 (URL: https://doi.org/10.18637/jss.v087.i11).

Please report bugs and suggestions on GitHub. Thank you!