最裏面的真值

Question

如果我有一個邏輯陣列，看起來像

x = c(TRUE, TRUE, FALSE, FALSE, FALSE, TRUE, TRUE, TRUE) 

什麼以獲得本例中的最內側TRUEs最簡單的方法，前述情況是在索引2和索引6

Answer 1

我不知道你的問題是明確定義的，但在這種特殊情況下，rle給你所需要的：

> rle(x)$lengths[1] 
[1] 2 
> rle(x)$lengths[1]+rle(x)$lengths[2]+1 
[1] 6 

Answer 2

，這可能是更強大的？如果trues和falses切換兩次以上，rle將不起作用。

# you could try it on the original vector.. 
    # x <- c(TRUE, TRUE, FALSE, FALSE, FALSE, TRUE, TRUE, TRUE) 

    # ..but it also works on a more scattered vector 
    x <- c(TRUE, FALSE , TRUE, FALSE, FALSE, FALSE, FALSE , TRUE, TRUE, TRUE) 

    # find the position of all TRUEs 
    true.positions <- which(x) 

    # find the midpoint of the vector 
    midpoint <- length(x)/2 

    # find the smallest distance from the midpoint, 
    small.dist <- (true.positions - midpoint) 

    # both above and below 
    small.dist.above <- min(small.dist[ small.dist >= 0 ]) 
    small.dist.below <- abs(max(small.dist[ small.dist <= 0 ])) 

    # find the lowest position above the midpoint 
    lpa <- which(small.dist.above == true.positions - midpoint) 
    # find the highest position below the midpoint 
    hpb <- which(small.dist.below == midpoint - true.positions) 

    # if both are the midpoint, combine them 
    closest.trues <- unique(c(hpb , lpa)) 

    # return the position in the original vector x 
    # of the innermost TRUE 
    true.positions[ closest.trues ]