Rmarkdown Htmltable in loop, "knit html" button different output than rmarkdown::render

Question

I'm working in RMarkdown, trying to render a document with htmltables from the htmlTable package in a loop. When I push the "Knit" button in RStudio, everything works great. But when I use the render() function, the htmltables in the loop don't get printed, but the table just before the loop does. I read that "knit" button and the render function does the same, so I don't understand whats wrong?

This is a working example of a .Rmd file with a hmtlTables:

---
output: html_document
---

## htmlTables


```{r, results='asis'}
library(data.table)
library(htmlTable)
library(ggplot2)
a <- data.table(matrix(seq(1, 100, 5), ncol = 2))
htmlTable(a)
for (i in 10:11) {
    cat( paste('## title no.', i, '\n' ) ) 
    print(ggplot(a*i, aes(x = V1, y = V2)) + geom_point())
    print(htmlTable(a*i))
    cat('\n')
}
```

I need to generate many reports automatically with different parameters, so I need to get this working with render().

Answer 1

htmlTable has defined a print method, which appears to print the table in a new window, change print() to writeLines() will do the trick:

---
output: html_document
---

## htmlTables


```{r, results='asis'}
library(data.table)
library(htmlTable)
library(ggplot2)
a <- data.table(matrix(seq(1, 100, 5), ncol = 2))
htmlTable(a)
for (i in 10:11) {
    cat( paste('## title no.', i, '\n' ) ) 
    print(ggplot(a*i, aes(x = V1, y = V2)) + geom_point())
    writeLines(htmlTable(a*i))
    cat('\n')
}
```

---

However it still seems a bit strange to me because I believe that the knit button uses rmarkdown::render() under the hood but they have different behaviors in this case.