signif() + datatable() bug

[le-raman]

Hi devs,

Reporting following bug, using R v4.3.2 and DT v0.27.

DT::datatable(signif(data.frame(3.234866680561728e-127), 3))

I expected:

But got:

Any idea what causes this?

[yihui]

I think this is a problem on htmltools or htmlwidgets's side. The data is correct on DT's side:

> x = DT::datatable(signif(data.frame(3.234866680561728e-127), 3))
> str(x)
List of 8
 $ x            :List of 6
  ..$ filter   : chr "none"
  ..$ vertical : logi FALSE
  ..$ data     :'data.frame':	1 obs. of  2 variables:
  .. ..$                       : chr "1"
  .. ..$ X3.23486668056173e.127: num 3.23e-127
[...]

but 3.23e-127 is converted to 3.229999999999999e-127 when the widget is rendered to HTML:

> str(htmlwidgets:::toHTML(x))
List of 3
 $ :List of 3
  ..$ : NULL
  ..$ :List of 3
  .. ..$ name    : chr "div"
[...]
 $ :List of 3
  ..$ name    : chr "script"
  ..$ attribs :List of 2
  .. ..$ type    : chr "application/json"
  .. ..$ data-for: chr "htmlwidget-6b6194a1b92c04b274c8"
  ..$ children:List of 1
  .. ..$ : 'html' chr "{\"x\":{\"filter\":\"none\",\"vertical\":false,\"data\":[[\"1\"],[3.229999999999999e-127]],\"container\":\"<tab"| __truncated__
  .. .. ..- attr(*, "html")= logi TRUE

[le-raman]

I see, thanks for the response. The strange thing, it doesn't happen when directly running DT::datatable(signif(data.frame(3.23e-127), 3)). Anyway, I switched to using %>% DT::formatSignif(... which solves my issue.

[jcheng5]

Unfortunately I think this is just a natural consequence of floating point imprecision. (I couldn't reproduce DT::datatable(signif(data.frame(3.23e-127), 3)) looking "correct"--on my machine it looked the same as the first case.)

> print(signif(3.23e-127, 3), digits=16)
[1] 3.229999999999999e-127

R defaults to precision of digits=7 when printing, while htmlwidgets defaults to digits=16 when serializing to the browser. The idea in theory is that the value should be transmitted with max precision, but when actually displayed in the web page you can use less precision. Unfortunately I can't think of a single htmlwidget that goes out of its way to display with fewer digits.

I don't know if it's a good idea to do so, but you can use options(shiny.json.digits = xxx) to set the precision to whatever you want. This gets passed to the jsonlite::toJSON() function's digits argument.