如何在R中返回序列的行索引? [英] How do I return the row index of a sequence in R?

问题描述

我正在尝试查找序列的行位置.我的意思是:

I'm trying to find the row positions of a sequence. By that I mean the following:

x<-c(-1,1)
y<-c(1,-1,1,0,-1,0,0)
match(x,y)
[1] 2 1

为什么这不返回2 3? (这就是我想要的)

Why doesn't this return 2 3 ? (That's what I want it to do)

如果我这样做:

y<-c(0,-1,1,0,-1,0,0)
match(x,y)
[1] 2 3

有效.咨询吗?

推荐答案

这是个主意.如果有多个匹配项，imatch()将找到所有个匹配的索引.它通过检查两个连续的索引(一次一对)并检查它们是否与x向量相同来做到这一点.不匹配项将被删除，并返回匹配项列表.

Here's an idea. imatch() will find all the matched indices, in case there is more than one set of matches. It does this by checking two successive indices, one pair at a time, and checking if they are identical to the x vector. Non-matches are removed, and a list of matches returned.

imatch <- function(x, y) {
    Filter(
        Negate(is.null), 
        lapply(seq_along(length(y)-1), function(i) {
            ind <- i:(i+1)
            if(identical(y[ind], x)) ind 
        })
    )
}

imatch(c(-1, 1), c(1, -1, 1, 0, -1, 0, 0))
# [[1]]
# [1] 2 3

imatch(c(-1, 1), c(1, -1, 1, 0, -1, 1, 0))
# [[1]]
# [1] 2 3
#
# [[2]]
# [1] 5 6

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