'printing' HTML widgets in programmatically generated Rmarkdown

Question

I'm trying to programmatically generate some Rmarkdown and one of the sections contains an HTML widget. These are output fine if they are last in my function. However, if I wrap them in a print so I can put something else after them as you would do for a plot they do not produce any output.

Perhaps this some something to do with the way knitr handles printing i'm not sure. But does anyone know how I can get HTML widgets to behave like plots do in programmatically generated Rmarkdown?

Example .Rmd

---
title: "R Notebook"
output:
  html_document:
    df_print: paged
---

```{r}
ex_plot <- ggplot2::ggplot(iris, ggplot2::aes(Sepal.Length,Sepal.Width)) + 
    ggplot2::geom_point()

gen_rmarkdown_widget_last <- function() {
    cat("# Head 1\n\n")
    DT::datatable(iris)
}

gen_rmarkdown_plots <- function() {
    cat("# Head 1\n\n")
    print(ex_plot)
    cat("# Head 2\n\n")
}

gen_rmarkdown_widgets <- function() {
    cat("# Head 1\n\n")
    print(DT::datatable(iris))

    # tried loading from file
    # tmp <- tempfile()
    # htmlwidgets::saveWidget(DT::datatable(iris), tmp)
    # knitr::include_url(tmp)
    
    # tried a different widget
    # print(plotly::ggplotly(ex_plot))

    cat("# Head 2\n\n")
}

```

```{r, results='asis'}
# works fine
gen_rmarkdown_widget_last()
```

```{r, results='asis'}
# works fine
gen_rmarkdown_plots()
```

```{r, results='asis'}
# Can't have an HTML widget if it is followed by other things
gen_rmarkdown_widgets()
```

Try `print(htmltools::tagList(DT::datatable(iris)))`. Looks related to https://stackoverflow.com/questions/63532652/printing-any-number-of-dataframes-stored-in-list-as-paged-tables-in-rmarkdown/63533860#63533860 — stefan, Oct 19 '20 at 15:32
Interesting that adds an empty space where the widget would go between the headings but does not output the widget... — Richard J. Acton, Oct 19 '20 at 15:48
Hm Weird. I tested it on my machine. When I run your code just the headers get printed. Using `print(htmltools::tagList(DT::datatable(iris)))` outputs the DT after Head 1, followed by Head 2. — stefan, Oct 19 '20 at 15:51
fascinating if I only run the `gen_rmarkdown_widgets` with your suggestion it does not work if I run working example `gen_rmarkdown_widget_last` first then `gen_rmarkdown_widgets` if works. Must be something to do with that initialisation thing mentioned in the post you linked to — Richard J. Acton, Oct 19 '20 at 15:56
Yep. Initalising is important to include the JS dependencies in the final HTML document. — stefan, Oct 19 '20 at 16:04
Do you know of a way to 'manually' initialise the widget so that the appropriate JS is included in the document without making a call to DT or other widget that is not 'cached' in the `print`/`tagList` call and thus apparently not noticed by whatever `knitr` is doing to decide what JS to include? — Richard J. Acton, Oct 19 '20 at 16:09
I mean you can just stick a chunk like this in that seem very hackey: ```{r, include=FALSE, echo=FALSE} DT::datatable(data.frame()) plotly::ggplotly(ggplot2::ggplot()) ``` — Richard J. Acton, Oct 19 '20 at 16:20
Haven't tried it myself. But I guess you could add some HTML to include the JS dependencies yourself. — stefan, Oct 19 '20 at 16:52

Waldi · Accepted Answer · 2020-10-21T15:05:33.500

The issue has been discussed here.

Adding the dependencies manually is done with:

data.frame() %>%
  DT::datatable() %>%
  knitr::knit_print() %>%
  attr('knit_meta') %>%
  knitr::knit_meta_add() %>%
  invisible()

In the example you provided:

---
title: "R Notebook"
output:
  html_document:
    df_print: paged
---

```{r}
library(dplyr)
#load dependencies
data.frame() %>%
  DT::datatable() %>%
  knitr::knit_print() %>%
  attr('knit_meta') %>%
  knitr::knit_meta_add() %>%
  invisible()

ex_plot <- ggplot2::ggplot(iris, ggplot2::aes(Sepal.Length,Sepal.Width)) + 
    ggplot2::geom_point()



gen_rmarkdown_widget_last <- function() {
    cat("# Head 1\n\n")
    DT::datatable(iris)
}

gen_rmarkdown_plots <- function() {
    cat("# Head 1\n\n")
    print(ex_plot)
    cat("# Head 2\n\n")
}

gen_rmarkdown_widgets <- function() {
    cat("# Head 1\n\n")
    cat(knitr::knit_print(DT::datatable(iris)))
    cat("\n  \n")
    cat("# Head 2\n\n")
}

```


```{r, results='asis'}
gen_rmarkdown_widgets()
```

'printing' HTML widgets in programmatically generated Rmarkdown

1 Answers1

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