[R] How to spot/stop making the same mistake

[Jeff Newmiller]

For the record, `!!` is not an operator so it does not "operate" on anything. The right ! does per the help page (?`!`) interpret non-zero values as TRUE and invert that logic, yielding a logical result even if the input is not logical. The left ! inverts that again, yielding a logical vector without the inversion.

On June 23, 2021 10:39:07 AM PDT, Phillips Rogfield <thebudget72 using gmail.com> wrote:
>Dear all,
>
>thank for for your suggestion.
>
>Yes I come from languages where 1 means TRUE and 0 means FALSE. In 
>particular from C/C++ and Python.
>
>Evidently this is not the case for R.
>
>In my mind I kind took for granted that that was the case (1=TRUE,
>0=FALSE).
>
>Knowing this is not the case for R makes things simpler.
>
>Mine was just an example, sometimes I load datasets taken from outside 
>and variables are coded with 1/0 (for example, a treatment variable may
>
>be coded that way).
>
>I also did not know the !!() syntax!
>
>Thank you for your help and best regards.
>
>On 23/06/2021 17:55, Bert Gunter wrote:
>> Just as a way to save a bit of typing, instead of
>>
>> > as.logical(0:4)
>> [1] FALSE  TRUE  TRUE  TRUE  TRUE
>>
>> > !!(0:4)
>> [1] FALSE  TRUE  TRUE  TRUE  TRUE
>>
>> DO NOTE that the parentheses in the second expression should never be
>
>> omitted, a possible reason to prefer the as.logical() construction.
>> Also note that !!  "acts [only] on raw, logical and number-like 
>> vectors," whereas as.logical() is more general. e.g. (from ?logical):
>>
>> > charvec <- c("FALSE", "F", "False", "false",    "fAlse", "0",
>> +              "TRUE",  "T", "True",  "true",     "tRue",  "1")
>> > as.logical(charvec)
>>  [1] FALSE FALSE FALSE FALSE    NA    NA  TRUE  TRUE  TRUE  TRUE  
> NA 
>>    NA
>> > !!charvec
>> Error in !charvec : invalid argument type
>>
>>
>> Cheers,
>> Bert
>>
>> Bert Gunter
>>
>> "The trouble with having an open mind is that people keep coming
>along 
>> and sticking things into it."
>> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
>>
>>
>> On Wed, Jun 23, 2021 at 8:31 AM Eric Berger <ericjberger using gmail.com 
>> <mailto:ericjberger using gmail.com>> wrote:
>>
>>     In my code, instead of 't', I name a vector of indices with a
>>     meaningful
>>     name, such as idxV, to make it obvious.
>>
>>     Alternatively, a minor change in your style would be to replace
>your
>>     definition of t by
>>
>>     t <- as.logical(c(1,1,1,0,0))
>>
>>     HTH,
>>     Eric
>>
>>
>>     On Wed, Jun 23, 2021 at 6:11 PM Phillips Rogfield
>>     <thebudget72 using gmail.com <mailto:thebudget72 using gmail.com>>
>>     wrote:
>>
>>     > I make the same mistake all over again.
>>     >
>>     > In particular, suppose we have:
>>     >
>>     > a = c(1,2,3,4,5)
>>     >
>>     > and a variable that equals 1 for the elements I want to select:
>>     >
>>     > t = c(1,1,1,0,0)
>>     >
>>     > To select the first 3 elements.
>>     >
>>     > The problem is that
>>     >
>>     > a[t]
>>     >
>>     > would repeat the first element 3 times .....
>>     >
>>     > I have to either convert `t` to boolean:
>>     >
>>     > a[t==1]
>>     >
>>     > Or use `which`
>>     >
>>     > a[which(t==1)]
>>     >
>>     > How can I "spot" this error?
>>     >
>>     > It often happens in long scripts.
>>     >
>>     > Do I have to check the type each time?
>>     >
>>     > Do you have any suggestions?
>>     >
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>>     <http://www.R-project.org/posting-guide.html>
>>     > and provide commented, minimal, self-contained, reproducible
>code.
>>     >
>>
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>>
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>>     <http://www.R-project.org/posting-guide.html>
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>code.
>>
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>
>______________________________________________
>R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.

-- 
Sent from my phone. Please excuse my brevity.