multiple devices error

[gaospecial]

When set dev = c("png","pdf"), it will cause a error:

Error in suffix != "" && TRUE : 'length = 2' in coercion to 'logical(1)'

This PR fixed this problem.

[CLAassistant]

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[yihui]

This sounds reasonable, but I don't know how to reproduce the problem. I tested a simple code chunk and didn't see the error:

```{r, dev=c('png', 'pdf')}
plot(1)
```

Thanks!

[gaospecial]

I can't reproduce it, either. But I finally figured it out, because I added a opts_hook() to include download links in figure captions.

knitr::opts_chunk$set(
  fig.align = "center",
  warning = FALSE,
  message = FALSE,
  dev = c("png","pdf"),
  fig.ext = c("png", "pdf"),
  fig.width = 6.5,
  fig.asp = 0.618,
  fig.align = "center"
)

# add opts_hooks
knitr::opts_hooks$set(dev = function(options){
  if (length(options$dev) > 1){
    x = paste0("[", options$dev, "](", knitr::fig_path(options$dev), ")",
               collapse = " | ")
    options$fig.cap = paste(options$fig.cap, x, sep = " ")
  }
  options
})

It is my problem. I guess that knitr itself doesn't pass options$dev directly to fig_path(). It is knitter.

[yihui]

Even if it's your problem, I think the code change in this PR will be an improvement (the operation on suffix has been vectorized), so I'll merge it anyway.

[gaospecial]

OK. I agree. ^_^