R Markdown使用动态字符串扩展：无法启动png（）设备时出现错误，没有明确的原因有时

Question

I have this code in my dummy markdown script.

<!--- add tests from dynamic strings --> 
`r paste(knit(text = expand_string), collapse = '\n')`

The string is generated in a main script:

generate_expand_string <- function(reported_test)
{

     exp_str <- paste0(
          '<h2>',
          reported_test,
          '</h2>',
          '\n',
          '<br>',
          '\n```{r ',
          paste0(reported_test, '_charts'),
          ', echo = F, fig.width = 14, fig.height = 12, fig.align = "center", message = F, warning = F}\n\n',
          'current_test <- ',
          '"',
          reported_test,
          '"',
          '\n\n',
          'if(length(indicator_charts[[current_test]]) > 0) { for(i in 1:length(indicator_charts[[current_test]])) { print(indicator_charts[[current_test]][[i]]) } };',
          '\n\n```',
          '\n',
          '<br>',
          '\n```{r ',
          paste0(reported_test, '_table'),
          ', results = "asis", echo = F}\n\n',
          'current_test <- ',
          '"',
          reported_test,
          '"',
          '\n\n',
          'kable(indicator_tables[[current_test]], align = rep("l", times = ncol(indicator_tables[[current_test]])));',
          '\n\n```',
          '\n\n'
     )

     return(exp_str)

}

And I run markdown inside the main script:

rmarkdown::render(
               paste0(
                    getwd(),
                    '/',
                    'dfsdsvcg/',
                    dfsfdsfdf
               ),
               output_file = paste0(
                    gsub(' ', '_', reported_indicator),
                    entity_indicator_report_file_name
               ),
               output_dir = out_dir
          )

I actually checked the existence of a folder where the png images are temporally stored:

<img src="S:\dfdfdf\dffdfd\debug\detailed\entities\September_2017\15_September_2017\thtthththef-addons\bwagfewcdvfe_files/figure-html/njebgkrded_charts-1.png" width="1344" style="display: block; margin: auto;" />

Looks like this. There are the images. And this error happens 1 / 500 times as I generate the pages in a loop.

Question: what do you think could cause it?

I have a guess when this happens: the path length to image becomes 200+ characters long. I can try make it shorter.

Answer 1

Answer (apparently the cause of the bug fixing which worked for me): if the path length to images exported from a listed ggplot object as png files and stored temporally in a report directory becomes larger than n elements (around 200) the report generation in Markdown fails. Take care about your output file name lengths.