computeDistIdx.RdcomputeDistIdx computes the indices of entries in a
distance matrix (as computed by dist) that hold
the distances between a given point and one or more other points.
computeDistIdx(n, i, j = setdiff(1:n, i), includeMyself = FALSE)
| n | number of points |
|---|---|
| i | index of point to compute distance from |
| j | index of point(s) to compute distance to |
| includeMyself | if TRUE, and |
a vector of indices of entries in the distance matrix related to
the distances from the i-th point to the other points.
The indices of entries corresponding to the distance between
point j and point i are sorted in increasing order
according to j. If includeMyself is TRUE,
the returned vector includes an extra NA element
corresponding to the non-existing index into the distance matrix
holding the distance between point i and point i
itself. This makes the length of the returned vector to be equal
to n, such that the index corresponding to the distance
between point i and point j resides at position
j in the returned vector.
x <- 1:10 d <- dist(x) # entries holding distances between the 3rd point and all the # other points computeDistIdx(length(x), 3)#> [1] 2 10 18 19 20 21 22 23 24# include an extra \code{NA} at the 3rd position to make the vector easily indexable i <- computeDistIdx(length(x), 3, includeMyself = TRUE) i#> [1] 2 10 NA 18 19 20 21 22 23 24# the distance between point 3 and 4: d[i[4]]#> [1] 1# entries holding distances between the 3rd point and points 5 and 7 computeDistIdx(length(x), 3, c(5, 7))#> [1] 19 21