How to knit_print flextable with loop in a rmd file

Question

I am trying to produce mutltiple tables using the flextable and kable packages. When I want to output some table iteratively, I found knit_print of flextable is not working in loop. Below is a minimal example:

---
output: word_document
---

```{r}
library(flextable)
library(knitr)
```

```{r}
 data(cars)
     speed<-unique(cars$speed)
for (v in 1:length(speed)) {
  carspd<-cars[which(cars$speed==speed[v]),]
  tb<-regulartable(carspd)
knit_print(tb)
}
knit_print(tb)
```

Just the last knit_print can print the result to the word_document with the .Rmd file.

---

Now I find the difference of them in .md which is output by the pandoc process file with ultraedit, the right table:

```{=openxml}
<w:tbl xmlns:w=".......

the wrong table:

鈥媊``{=openxml}
<w:tbl xmlns:w="

In hexadecimal there are extra content:"E2 80 8B", someone call they Zero-Width Space? But I am not figure out how to avoid it.

Answer 1

This is a limitation of one of the functions that flextable uses in its knit_print method: knitr::asis_output() can't be used in a loop. A couple of solutions are described here: https://github.com/yihui/knitr/issues/1137.

This one works for me in HTML output, just collecting all the output into one big vector and printing it at the end. I have modified the code to also insert some text before the table and a figure after it. I don't use Word, but I'd assume it will also work there:

---
output: html_document
---

```{r}
library(flextable)
library(knitr)
```

```{r}
data(cars)
speed <- unique(cars$speed)
results <- character()
for (v in 1:length(speed)) {
  carspd <- cars[which(cars$speed == speed[v]),]
  tb <- regulartable(carspd)

  # Generate a figure in a temporary file
  filename <- tempfile(fileext = ".png")
  png(filename)
  hist(carspd$dist)
  dev.off()

  # Put everything into the results vector
  results <- c(results, "\n\nThis is the table for v =", v,
                        knit_print(tb),
                        knitr:::wrap(include_graphics(filename)))

}
asis_output(results)
knit_print(tb)
```

A couple of notes:

• The \n\n in the text seems to be necessary to insert a line break.
• The knitr:::wrap() function is an undocumented internal function in knitr, so there might be limitations that I don't know about, and this might fail in some future version of knitr.