R中的上三角矩阵的外部函数 [英] Outer function in R for upper triangular matrix
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问题描述
我目前有此代码
s1=seq(0,10,length.out=3)
s2=seq(0,10,length.out=3)
d=outer(s1,s2,`-`)
I=outer(s1,s2,`==`)
但是我只想要d
的上三角,所以我目前正在做
However I only want the upper triangular of d
and I so I am currently doing
d=d[upper.tri(d,diag=T)]
I=I[upper.tri(I,diag=T)]
是否可以通过在外部函数中合并上三角矩阵来使此代码更快? 请注意,这是一个可重现的示例,但是我的代码更大,并且我需要尽可能减少运行时间.
Is there a way to make this code faster through incorporating the upper triangular matrix in the outer function? Note that this is a reproducible example, however my code is much bigger and I need to decrease the running time as much as possible.
推荐答案
outer
在内部使用rep
扩展其参数:
outer
internally uses rep
to stretch its arguments:
Y <- rep(Y, rep.int(length(X), length(Y)))
if (length(X))
X <- rep(X, times = ceiling(length(Y)/length(X)))
您可以使用子集执行相同的操作,但是仅生成三角索引. sequence
在这种情况下是有用的辅助功能:
You can do the same thing using subsetting, but instead generate only the triangular indices. sequence
is a useful helper function in this case:
> i <- sequence(1:3)
> j <- rep(1:3, 1:3)
> d = s1[i] - s2[j]
> I = s1[i] == s2[j]
> d
[1] 0 -5 0 -10 -5 0
> I
[1] TRUE FALSE TRUE FALSE FALSE TRUE
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