[Rd] diag(-1) produces weird result

[Gábor Csárdi]

Some languages that recognized early design mistakes introduced a
strict mode, which applies to a local context, and enforces a safer,
more consistent API. This is a pragmatic solution, as it does not
require any changes to existing code, but still allows writing better
code in the future.

Implementing a context restricted strict mode is probably not trivial,
considering the flexibility of the language, but maybe it is worth
some thinking.

Gábor
On Tue, Sep 18, 2018 at 2:00 PM peter dalgaard <pdalgd using gmail.com> wrote:
>
> Yes, both are rooted in age-old design infelicities (in which, basically, interactive expedience has taken precedence over consistency and generality).
>
> Unfortunately, they are quite difficult to rectify, because there are bound to be countless uses of, say, diag(5) as a 5x5 identity matrix which would break if it suddenly meant the 1x1 matrix(5) instead.
>
> We'd need a very carefully orchestrated warn-deprecate-defunct-newBehaviour sequence, with a time scale of years, most likely. It is, in principle, doable (I think), but we don't really have the mechanisms to follow through on it.  Almost all developers have main job responsibilities, and it is very easy to get sidetracked at the wrong moment, so most changes get done on a now-or-never basis.
>
> I have toyed with the idea of setting up for version-dependent code where code sections could be coded up front and then activated when the relevant version is reached. Then I got swamped again...
>
> -pd
>
> > On 17 Sep 2018, at 20:08 , Barry Rowlingson <b.rowlingson using lancaster.ac.uk> wrote:
> >
> > On Mon, Sep 17, 2018 at 5:22 PM, Gábor Csárdi <csardi.gabor using gmail.com>
> > wrote:
> >
> >> I would say it is a mis-feature. If the 'x' argument of diag() is a
> >> vector of length 1, then it creates an identity matrix of that size,
> >> instead of creating a 1x1 matrix with the given value:
> >>
> >> ❯ diag(3)
> >>     [,1] [,2] [,3]
> >> [1,]    1    0    0
> >> [2,]    0    1    0
> >> [3,]    0    0    1
> >>
> >> Of course this makes it cumbersome to use diag() in a package, when
> >> you are not sure if the input vector is longer than 1. This seems to
> >> be a good workaround:
> >>
> >> ❯ diag(-1, nrow = 1)
> >>     [,1]
> >> [1,]   -1
> >>
> >> Or, in general if you have vector v:
> >>
> >> ❯ v <- -1
> >> ❯ diag(v, nrow = length(v))
> >>     [,1]
> >> [1,]   -1
> >>>
> >>
> >
> > Anyone else getting deja-vu with the `sample` function?
> >
> >> sample(5:3)
> > [1] 3 5 4
> >
> > ok...
> >
> >> sample(5:4)
> > [1] 4 5
> >
> > fine...
> >
> >> sample(5:5)
> > [1] 3 1 5 2 4
> >
> > uh oh. Documented, of course.
> >
> > B
> >
> >       [[alternative HTML version deleted]]
> >
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>
> --
> Peter Dalgaard, Professor,
> Center for Statistics, Copenhagen Business School
> Solbjerg Plads 3, 2000 Frederiksberg, Denmark
> Phone: (+45)38153501
> Office: A 4.23
> Email: pd.mes using cbs.dk  Priv: PDalgd using gmail.com
>
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