[R] built a lower triangular matrix from dataframe

[R. Michael Weylandt]

I didn't think through mine all the way -- you do need the cbind()
call to do the indexing like I was thinking -- so mine when corrected
just turns into David's.

Michael

On Thu, Feb 16, 2012 at 5:26 AM, nymphita
<sandrablazquezcabrera at gmail.com> wrote:
> Hi Michael,
> Your answer was very interesting, thank you!
> However, I tried it and the result was:
>
>> df <- read.table(file="df.txt", head=T, sep="\t")
>> df
>   i j   k
> 1  1 2 5.2
> 2  1 3 9.1
> 3  1 4 8.0
> 4  1 5 2.3
> 5  1 6 8.4
> 6  2 3 6.6
> 7  2 4 7.4
> 8  2 5 7.1
> 9  2 6 5.5
> 10 3 4 4.1
> 11 3 5 3.9
> 12 3 6 9.2
> 13 4 5 8.5
> 14 4 6 7.6
> 15 5 6 9.9
>> x <- with(df, matrix(NA, ncol= max(j), nrow=max(i)+1))
>> x[with(df, i), with(df, j)] <- with(df, k)
>> x
>     [,1] [,2] [,3] [,4] [,5] [,6]
> [1,]   NA  8.4 8.4 8.4 8.4 8.4
> [2,]   NA  5.5  5.5  5.5  5.5  5.5
> [3,]   NA  9.2 9.2 9.2 9.2 9.2
> [4,]   NA  7.6  7.6  7.6  7.6  7.6
> [5,]   NA  9.9  9.9  9.9  9.9  9.9
> [6,]   NA   NA   NA   NA   NA   NA
>
> It seems that R only reads the values [1,6], [2,6], [3,6], [4,6], and [5,6]
> and repeats them for every postition of the row...
> Still trying to find why and how to change it, but if someone finds a
> solution it will be appreciated
>
> --
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