[R] "unfurling" rankings into a matrix of preferences

[Bert Gunter]

## I leave it to you to add the NA edges

> rk <- c(2,4,3,1)

> outer(rk,rk,"<")+0

     [,1] [,2] [,3] [,4]
[1,]    0    1    1    0
[2,]    0    0    0    0
[3,]    0    1    0    0
[4,]    1    1    1    0



Cheers,
Bert

Bert Gunter

"Data is not information. Information is not knowledge. And knowledge
is certainly not wisdom."
   -- Clifford Stoll


On Mon, Jul 27, 2015 at 12:38 PM, Dimitri Liakhovitski
<dimitri.liakhovitski at gmail.com> wrote:
> I have 5 items in total (1:5), but I show a person only 4 items (1:4)
> and ask this person to rank items 1:4 in terms of preferences (1 is
> best, 2 is second best, 4 is worst), and I get a vector of ranks:
> ranks <- c(2,4,3,1)
>
> # That means that this person liked item 4 best and item 2 worst.
>
> I would like to "unfirl" this vector of ranks into a matrix of
> preferences where if the row item prefers the column item, then it's a
> 1. Otherwise, it's a zero. So, the output should be a 5 by 5 matrix
> (because overall we have 5 items, not 4, but item 5 did not
> participate in rankings), and it would always have zeros in a
> diagonal.:
>
> 0    1    1    0 NA
> 0    0    0    0 NA
> 0    1    0    0 NA
> 1    1    1    0 NA
> NA NA NA NA 0
>
> I can loop through all possible pairs the person saw and fill the
> matrix accordingly, but it seems like a lot of looping. Could one do
> it in a more elegant way?
>
> Thank you very much!
>
>
> --
> Dimitri Liakhovitski
>
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