用于测试短数字向量是否是R中长数字向量的一部分的函数

Question

我试图测试一个短数字向量是否是一个较长的数字向量的一部分.例如,如果a = c(2, 3)和b = c(1, 3, 2, 4, 2, 3, 1),那么我试图找到/想到一个能回答这个问题的函数:是a一部分b吗？输出应该是TRUE.

或者,如果c = c(1, 3, 2, 4, 1, 3, 1)那时输出"是？a的一部分c？" 应该是FALSE.

match() 不做这个工作:

match(a, b)

回报

3  2

%in%运营商也不是:

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

这是我对它的抨击

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)

Answer 2

这是一次尝试.我不认为它超级快,但它也不是超慢:

a  = c(2,3)
b1 = c(1, 3, 2, 4, 2, 3, 1)
b2 = c(1, 3, 2, 4, 1, 3, 1)

ainb <- function(a,b) {
  any(apply( embed(b,length(a)), 1, function(x) all(rev(a)==x) ))
}
ainb(a,b1)
#[1] TRUE
ainb(a,b2)
#[1] FALSE