Extension to knitr/Rmarkdown to ignore only specific warnings (not all) in a chunk
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@wolfgang-huber-3550
Last seen 3 months ago
EMBL European Molecular Biology Laborat…

Is there already an extension to knitr/Rmarkdown that instead of 'warning=FALSE' lets you specify which warnings should be suppressed/ignored (and thus, which others not)?

I want to take precautions against code rot in a very large and possibly long-lived document.

rmarkdown suppressWarning warning • 1.9k views
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Mike Smith ★ 6.4k
@mike-smith
Last seen 11 hours ago
EMBL Heidelberg

This requires some refinement, but how about modifying the knitr::knit_hooks for "warnings" to search each warning for known patterns and only printing those that aren't found e.g.

---
title: "Untitled"
author: "Mike Smith"
date: "12/8/2021"
output: html_document
---

```{r setup, include=FALSE}
knitr::knit_hooks$set(warning = function(x, options) { 

    if(options$warning == TRUE) {
        sprintf('<div class="warning"><pre class="knitr %s">%s</pre></div>\n', tolower(options$engine), x)
    } else {
        known_warning <- any(vapply(options$warning, 
                                FUN = grepl, 
                                FUN.VALUE = logical(1), 
                                x = x))
        if(!known_warning) {
            sprintf('<div class="warning"><pre class="knitr %s">%s</pre></div>\n', tolower(options$engine), x)
        }
    }

})
```

## Default warning handling

```{r, warning = TRUE}
1:2 + 3:5
```

## Suppress known warning

```{r, warning = c("longer object length")}
1:2 + 3:5
```

## Suppress known warning, but print new warning

```{r, warning = c("longer object length")}
1:2 + 3:5
testit <- function() warning("testit")
testit()
```

which renders to:

enter image description here

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@wolfgang-huber-3550
Last seen 3 months ago
EMBL European Molecular Biology Laborat…

Thank you, Mike! Here, in case anyone else is interested, is the code I am now using for the MSMB book. It addresses the fact that both x and options$warning can be vectors, and cleans up gratuitous formatting inserted by knit.

cleanup = function(x) gsub("\n#*", "", gsub("^## ", "", x))

knitr::knit_hooks$set(warning = function(x, options) {
  ow   = options$warning
  x    = cleanup(unique(x)) 
  keep = if (is.character(ow) && length(ow) > 0) {
           res = rep(TRUE, length(x))
           for (w in ow)
             res = res & !grepl(w, x, ignore.case = TRUE)
           res
         } else if(is.logical(ow) && length(ow)==1) {
           rep(ow, length(x))
         } else {
           stop("In knit hook for warning, do not know how to handle 'options$warning'.")
         }

  if (any(keep))
    sprintf('<div class="warning"><pre class="knitr %s">%s</pre></div>\n', tolower(options$engine), x[keep])
})

It is then used in code chunks like in the following example.

```{r dbscanfcs, warning = c("stat_contour..: Zero contours were generated", "min.x.: no non-missing arguments to min; returning Inf", "max.x.: no non-missing arguments to max; returning -Inf")}
res5 = dbscan::dbscan(mc5, eps = 0.65, minPts = 30)
mc5df = data.frame(mc5, cluster = as.factor(res5$cluster))
ggplot(mc5df, aes(x = CD4, y = CD8,  col = cluster)) + geom_density2d()
```
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This approach no longer works following the release of knitr 1.42 and evaluate 0.19. The warning chunk option is expecting a logical, and the above approach fortuitously worked; it now breaks following the release of those two packages.

We now use a new chunk option warning.known to pass the vector of expected warnings. The updated hook is:

knitr::knit_hooks$set(
  warning = function(x, options) {
    ow   = options$warning.known
    if(is.null(ow)) ow <- options$warning
    x    = unique(x)
    keep = if (is.character(ow) && length(ow) > 0) {
      res = rep(TRUE, length(x))
      for (w in ow)
        res = res & !grepl(w, x, ignore.case = TRUE)
      res
    } else if (is.logical(ow) && length(ow) == 1) {
      rep(ow, length(x))
    } else {
      NA   
    }
    sprintf(
      '<div class="warning"><pre class="knitr %s">%s</pre></div>\n',
      tolower(options$engine),
      if (is.na(keep))
        "In knitr hook for warning, do not know how to handle 'options$warning'."
      else if (any(keep))
        paste(sprintf("In chunk '%s': ", options$label), x[keep], sep = "")
      else
        character(0)
    ) 
  }
)

The following code block will only report the warning "baz" in the output document.

```r
#| warning: TRUE
#| warning.known: !expr c("foo", "bar")
warning("foo")
warning("bar")
warning("baz")
```

If warning.known isn't set, the behaviour is still dictated by the knitr standard warning option.

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