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

[Bert Gunter]

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> 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>
> 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?
> >
> > ______________________________________________
> > 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.
> >
>
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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.
>

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