【描述】

找出你给的参数里逻辑值为TRUE的元素的索引

【用法】

which(x, arr.ind = FALSE, useNames = TRUE)
arrayInd(ind, .dim, .dimnames = NULL, useNames = FALSE)

【参数】

x   
a logical vector or array. NAs are allowed and omitted (treated as if FALSE).

arr.ind 
logical; should array indices be returned when x is an array?

ind 
integer-valued index vector, as resulting from which(x).

.dim    
dim(.) integer vector

.dimnames   
optional list of character dimnames(.). If useNames is true, to be used for constructing dimnames for arrayInd() (and hence, which(*, arr.ind=TRUE)). If names(.dimnames) is not empty, these are used as column names. .dimnames[[1]] is used as row names.

useNames    
logical indicating if the value of arrayInd() should have (non-null) dimnames at all.

【代码】

> x <- seq(1:10)
> x
 [1]  1  2  3  4  5  6  7  8  9 10
> which(x != 5)
[1]  1  2  3  4  6  7  8  9 10

> which(c(T,F,T))
[1] 1 3