R pairwise product

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庸人自扰
庸人自扰 2021-01-18 15:25

I\'m trying to get the pairwise products of a vector, say

a = c(1,2,3,4)

What I\'m trying to get is

2,3,4,6,8,12 (in that order).<

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  • 2021-01-18 15:58

    combn() is nice for this sort of thing:

    a <- 1:4
    
    combn(a, m = 2, FUN = prod) 
    # [1]  2  3  4  6  8 12
    
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  • 2021-01-18 16:02

    lower.tri selects them in that order:

    out <- outer(1:4,1:4)
    out[lower.tri(out)]
    # [1]  2  3  4  6  8 12
    
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