[Rd] diag(-1) produces weird result

[Gábor Csárdi]

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

Gabor
On Mon, Sep 17, 2018 at 5:14 PM William Revelle <lists using revelle.net> wrote:
>
> Dear list
>
> A strange bug in the psych package is due to the behavior of the diag function:
>
> It gives the expected values for 1, a vector (-1,1), but not for -1
>
> Is this a known feature?
>
>
> > diag(1)
>      [,1]
> [1,]    1
> > diag(c(-1,1))
>      [,1] [,2]
> [1,]   -1    0
> [2,]    0    1
> > diag(-1)
> Error in diag(-1) : invalid 'nrow' value (< 0)
>
>
> Bill
>
>
> William Revelle            personality-project.org/revelle.html
> Professor                                 personality-project.org
> Department of Psychology www.wcas.northwestern.edu/psych/
> Northwestern University    www.northwestern.edu/
> Use R for psychology         personality-project.org/r
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