multiple (R) plotly figures generated in a Rmarkdown (knitr chunk) document

Question

I try to create multiple plotly figures in a Rmarkdown document using loop or lapply.

The R script:

require(plotly)
data(iris)
b <- lapply(setdiff(names(iris), c("Sepal.Length","Species")),
            function(x) {
              plot_ly(iris, 
                      x = iris[["Sepal.Length"]],
                      y = iris[[x]], 
                      mode = "markers")
            })
print(b)

works well, but it fails when included in a knitr chunk:

---
output: html_document
---

```{r,results='asis'}
require(plotly)
data(iris)
b <- lapply(setdiff(names(iris), c("Sepal.Length","Species")),
            function(x) {
              plot_ly(iris, 
                      x = iris[["Sepal.Length"]],
                      y = iris[[x]], 
                      mode = "markers")
            })
print(b)
```

I tried replacing print(b) with a combination of lapply eval and parse but only the last figure was displayed.

I suspect a scoping/environment issue but I cannot find any solution.

Answer 1

Instead of print(b), put b in htmltools::tagList(), e.g.

```{r}
library(plotly)

b <- lapply(
  setdiff(names(iris),
          c("Sepal.Length","Species")),
  function(x) {
    plot_ly(iris, 
            x = iris[["Sepal.Length"]],
            y = iris[[x]], 
            mode = "markers")
  }
)

htmltools::tagList(b)
```

Note: Before Plotly v4 it was necessary to convert the Plotly objects to htmlwidgets using Plotly's as.widget() function. As of Plotly v4 they are htmlwiget objects by default.

For people who are interested in the technical background, you may see this blog post of mine. In short, only top-level expressions get printed.