[RkWard-devel] Length and NAs

[Thomas Friedrichsmeier]

Hi,

especially Stefan will hate me for this, but when reviewing some of the 
moments tests, I came across this issue, which applies to a whole lot of 
plugins:

I think there is a bit of a usability problem with the "length" option(s): The 
problem is that it's not immediately obvious, whether the length shown is the 
length including NAs, or without NAs. I think it's especially pronounced, 
when length is shown, but NAs are not. In this case, I think a reasonable 
assumption for a user would be to think that this is the length excluding any 
NAs. 

To alleviate this problem, I suggest a relatively simple solution, which would 
have to be applied to a whole lot of plugins, however: Instead of providing 
separate options for showing length and NAs, provide just one option, which 
will show or hide both values at once. The reasoning is, that if NAs are 
always shown alongside length, the user should at least become aware of the 
potential problem, and not jump to any (wrong) conclusions.

I'm willing to walk through all the existing plugins and change them 
accordingly. However, before I do so, I'd like to ask:
a) Any objections?
b) While I'm at it, should we perhaps change the length option(s) to show 
length excluding NAs, everywhere? I guess, probably not, but if you think we 
should, then now would be a good occasion to voice your preference.
c) Is there a good reason for keeping counting the NAs as
	length (which (is.na (x)))
? Otherwise I'd change this to
	sum (is.na (x))
which is shorter, and should be slightly more efficient.

Regards
Thomas
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