rstudio hangs and aborts with rmarkdown loop - r

Question

I have several datasets each of which have a common grouping factor. I want to produce one large report with separate sections for each grouping factor. Therefore I want to re-run a set of rmarkdown code for each iteration of the grouping factor.
Using the following approach from here doesnt work for me. i.e.:
---
title: "Untitled"
author: "Author"
output: html_document
---
```{r, results='asis'}
for (i in 1:2){
cat('\n')
cat("#This is a heading for ", i, "\n")
hist(cars[,i])
cat('\n')
}
```
Because the markdown I want to run on each grouping factor does not easily fit within one code chunk. The report must be ordered by grouping factor and I want to be able to come in and out of code chunks for each iteration over grouping factor.
So I went for calling an Rmd. with render using a loop from an Rscript for each grouping factor as found here:
# run a markdown file to summarise each one.
for(each_group in the_groups){
render("/Users/path/xx.Rmd",
output_format = "pdf_document",
output_file = paste0(each_group,"_report_", Sys.Date(),".pdf"),
output_dir = "/Users/path/folder")
}
My plan was to then combine the individual reports with pdftk. However, when I get to the about the 5th iteration my Rstudio session hangs and eventually aborts with a fatal error. I have ran individually the Rmd. for the grouping factors it stops at which work fine.
I tested some looping with the following simple test files:
.R
# load packages
library(knitr)
library(markdown)
library(rmarkdown)
# use first 5 rows of mtcars as example data
mtcars <- mtcars[1:5,]
# for each type of car in the data create a report
# these reports are saved in output_dir with the name specified by output_file
for (car in rep(unique(rownames(mtcars)), 100)){
# for pdf reports
rmarkdown::render(input = "/Users/xx/Desktop/2.Rmd",
output_format = "pdf_document",
output_file = paste("test_report_", car, Sys.Date(), ".pdf", sep=''),
output_dir = "/Users/xx/Desktop")
}
.Rmd
```{r, include = FALSE}
# packages
library(knitr)
library(markdown)
library(rmarkdown)
library(tidyr)
library(dplyr)
library(ggplot2)
```
```{r}
# limit data to car name that is currently specified by the loop
cars <- mtcars[rownames(mtcars)==car,]
# create example data for each car
x <- sample(1:10, 1)
cars <- do.call("rbind", replicate(x, cars, simplify = FALSE))
# create hypotheical lat and lon for each row in cars
cars$lat <- sapply(rownames(cars), function(x) round(runif(1, 30, 46), 3))
cars$lon <- sapply(rownames(cars), function(x) round(runif(1, -115, -80),3))
cars
```
Today is `r Sys.Date()`.
```{r}
# data table of cars sold
table <- xtable(cars[,c(1:2, 12:13)])
print(table, type="latex", comment = FALSE)
```
This works fine. So I also looked at memory pressure while running my actual loop over the Rmd. which gets very high.
Is there a way to reduce memory when looping over a render call to an Rmd. file?
Is there a better way to create a report for multiple grouping factors than looping over a render call to an Rmd. file, which doesn't rely on the entire loop being inside one code chunk?

Answer 1

Found a solution here rmarkdown::render() in a loop - cannot allocate vector of size
knitr::knit_meta(class=NULL, clean = TRUE)
use this line before the render line and it seems to work

Answer 2

I am dealing with the same issue now and it's very perplexing. I tried to create some simple MWEs but they loop successfully on occasion. So far, I've tried
Checking the garbage collection between iterations of rmarkdown::render. (They don't reveal any special accumulations.)
Removing all inessential objects
Deleting any cached files manually
Here is my question:
How can we debug hangs? Should we set up special log files to understand what's going wrong?