r - 测试短数值向量是否是 R 中长数值向量的一部分的函数

Question

我正在尝试测试一个短数值向量是否是一个较长数值向量的一部分。例如，如果 a = c(2, 3) 和 b = c(1, 3, 2, 4, 2, 3, 1)，那么我是试图找到/想出一个函数来回答这个问题:a 是 b 的一部分吗？输出应为 TRUE。

或者，如果 c = c(1, 3, 2, 4, 1, 3, 1) 那么“的输出是 a 的一部分>c?"应该是 FALSE。

match() 不做这个工作:

match(a, b)

返回

3  2

%in% 运算符也不行:

TRUE  TRUE

我知道有字符串匹配的选项，但我不想通过转换为字符串来解决这个问题...

Answer 1

这是我的绝招

valInLong <- function(val, long){
  n.long <- length(long)
  n.val <- length(val)
  # Find where in the longer vector the first
  # element of val is.  This is so we can vectorize later
  first <- which(long == val[1])
  # If the first element is too near the end we don't care
  # about it
  first <- first[first <= n.long - n.val + 1]
  # sequence from 0 to n.val - 1 used for grabbing subsequences
  se <- seq_along(val)-1
  # Look at all subsequences starting at 'first' that go
  # the length of val and do an elementwise comparison.
  # If any match in all positions then the subsequence is
  # the sequence of interest.
  any(sapply(first, function(x){all(long[x+se] == val)}))
}


long <- rpois(1000, 5)
a <- c(123421, 232, 23423) # probably not in long

valInLong(a, long)
a <- long[34:100]
valInLong(a, long)