[R] proportional matrix rows

[Liaw, Andy]

This works for your first example:

f <- function(m) {
    k <- t(t(m) %/% m[1,])
    which(rowSums(k - k[, 1]) == 0)
}

> f(jj)
[1] 1 2 8

but not the second one.  The 0s are problematic...

Andy


> From: Robin Hankin
> 
> Hi
> 
> I have a two-column integer matrix like this:
> 
> 
> R> jj
> 
>        [,1] [,2]
>   [1,]   -1    1
>   [2,]   -2    2
>   [3,]   -7    6
>   [4,]   -8    7
>   [5,]   -6    5
>   [6,]   -9    8
>   [7,]   -5    4
>   [8,]    3   -3
>   [9,]  -10    9
> [10,]   -4    3
> 
> I want a diagnostic that detects whether a row is a multiple of
> the first row or not.  In this case, this would be rows 1,2, and 8.
> 
> How to do this nicely?  Sometimes the first row has a zero, so the
> method would have to work on
> 
>       [,1] [,2]
> [1,]    0    1
> [2,]    1    1
> [3,]    0    8
> [4,]    0   -4
> [5,]    0    0
> [6,]    4    0
>  >
> 
> in which case rows 1,3,4,5 are multiples.  It'd be nice to have
> a solution that works for any number of columns.
> 
> --
> Robin Hankin
> Uncertainty Analyst
> Southampton Oceanography Centre
> European Way, Southampton SO14 3ZH, UK
>   tel  023-8059-7743
> 
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