Movatterモバイル変換

15.3.1 TheKnit button

By using theKnit button in RStudio or callingrmarkdown::render() function, the default values listed in the YAML metadata (if specified) will be used.

15.3.2 Knit with custom parameters

Even if your document has theparams field in the YAML metadata, you can actually override it by providing a custom list of parameter values to the functionrmarkdown::render(). For example:

rmarkdown::render("MyDocument.Rmd",params =list(year =2017,region ="Asia",printcode =FALSE,file ="file2.csv"))

We do not have to explicitly state all parameters in theparams argument. Any parameters not specified will default to the values specified in the YAML metadata. For example, this will only override theregion parameter:

rmarkdown::render("MyDocument.Rmd",params =list(region ="Asia"))

You may want to integrate these changes into a function. Such a function could also be used to create an output file with a different filename for each of the different combination of parameters. In the following example, a new fileReport-region-year.pdf is created for each set of parameters:

render_report=function(region, year) {  rmarkdown::render("MyDocument.Rmd",params =list(region = region,year = year    ),output_file =paste0("Report-", region,"-", year,".pdf")  )}

15.3.3 The interactive user interface

We can use a graphical user interface (GUI) based on Shiny to interactively input the parameters of a report. The user interface can be called by eitherrmarkdown::render("MyDocument.Rmd", params = "ask") or clicking the drop-down menu behind theKnit button and choosingKnit with Parameters in RStudio. Figure15.1 shows the GUI ofrmarkdown asking for inputting parameters.

FIGURE 15.1: Input parameter values interactively for parameterized reports.

The input controls for different types of parameters can be customized by specifying additional sub-items within the parameter specification in YAML. For example, sliders, check boxes, and text input boxes can all be used for input controls.

In addition, we can also specify constraints of the values allowed in each parameter. For example, we may only want our model to be run for years between 2010 and 2018. This is particularly beneficial if you would like other users to interact with the report, as it prevents users from attempting to run reports outside of the designed limits.

Adapting our above example to include some settings:

---title: My Documentoutput: html_documentparams:year:label:"Year"value:2017input: slidermin:2010max:2018step:1sep:""region:label:"Region:"value: Europeinput: selectchoices:[North America, Europe, Asia, Africa]printcode:label:"Display Code:"value:TRUEdata:label:"Input dataset:"value: results.csvinput: file---

This results in the user interface for the parameters as shown in Figure15.2.

FIGURE 15.2: Custom controls for parameters.

The type of Shiny control used is controlled by theinput field. Table15.1 shows the input types currently supported (see the help page for the associated Shiny function for additional attributes that can be specified to customize the input, e.g.,?shiny::checkboxInput).