检查 R 向量中的序列 [英] Checking for sequences in an R vector

问题描述

我正在寻找一个函数或操作，如果我有

I'm looking for a function or operation such that if I have

A <- c(1, 2, 3, 4, 5)

和B <- c(1, 2, 3)

和 C <- c(2, 1)

检查 A 是否包含 B 时得到 TRUE，检查 A 是否包含 C 时得到 FALSE

I'd get a TRUE when checking whether A contained B, and FALSE when checking whether A contained C

基本上相当于 %in% 运算符，但实际上关心元素的顺序

basically, the equivalent of the %in% operator but that actually cares about the order of elements

在一个完美的世界中，我可以在没有某种apply语句的情况下做到这一点，但我最终可能不得不

In a perfect world, I'd be able to do this without some kind of apply statement, but I may end up having to

推荐答案

好吧，如果允许使用某种应用循环，那么这可以工作:

Well, if one's allowd to use a kind-of apply loop, then this could work:

"%seq_in%" = function(b,a) any(sapply(1:(length(a)-length(b)+1),function(i) all(a[i:(i+length(b)-1)]==b))) 

(由于 John Coleman 的错误发现而编辑！)

(edited thanks to bug-finding by John Coleman!)

编辑 2:我也忍不住尝试解决不连续"的情况:

EDIT 2: I couldn't resist trying to solve the 'non-contiguous' case, too:

# find_subseq() returns positions within vec of ordered elements of x, or stops with NA upon failing
find_subseq = function(x,vec) {
    p=match(x[1],vec)
    if(is.na(p)||length(x)==1){ p } 
    else { c(p,p+find_subseq(x[-1],vec[-seq_len(p)])) }
}
"%seq_somewhere_in%" = function(b,a) all(!is.na(find_subseq(b,a)))

示例:

1:3 %seq_in% 1:10
[1] TRUE
c(3,1,2) %seq_in% 1:10
[1] FALSE
c(1,2,3) %seq_in% c(3,2,1,2,3)
[1] TRUE
2:1 %seq_in% c(1,2,1)
[1] TRUE
1:3 %seq_somewhere_in% c(1,10,10,2,10,10,10,3,10)
[1] TRUE

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