# duplicatedxy

##### Determine duplicated points.

Find which points among a given set are duplicates of others.

- Keywords
- utilities

##### Usage

`duplicatedxy(x, y)`

##### Arguments

- x
- Either a vector of
`x`

coordinates of a set of (two dimensional) points, or a list (or data frame) with columns`x`

and`y`

giving the coordinates of a set of such points. - y
- A vector of
`y`

coordinates of a set of (two dimensional) points. Ignored if`x`

is a list or data frame.

##### Details

Often it is of interest to associate each Dirichlet tile in a
tessellation of a planar point set with the point determining
the tile. This becomes problematic if there are *duplicate*
points in the set being tessellated/triangulated. Duplicated
points are automatically eliminated `deldir()`

but the association between tiles and the indices
of the original set of points is lost.

If it *is* of interest to associate Dirichlet tiles with the
points determining them it is better to proceed by eliminating
duplicate points to start with. This function provides a convenient
way of doing so.

##### Value

- A logical vector of length equal to the (original) number
of points being considered, with entries
`TRUE`

is the corresponding point is a duplicate of a point with a smaller index, and`FALSE`

otherwise.

##### Note

The real work is done by the base **R** function `duplicated()`

.

##### Warning

Which indices will be considered to be indices of duplicated
points (i.e. get `TRUE`

values) will of course depend on
the order in which the points are presented.

##### See Also

`duplicated()`

`deldir()`

##### Examples

```
set.seed(42)
xy <- data.frame(x=runif(20),y=runif(20))
# Lots of duplicated points.
xy <- rbind(xy,xy[sample(1:20,20,TRUE),])
# Scramble.
ii <- sample(1:40,40)
x <- xy$x[ii]
y <- xy$y[ii]
# Unduplicate!
iii <- !duplicatedxy(x,y)
xu <- x[iii]
yu <- y[iii]
# The i-th tile is determined by (xu[i],yu[i]):
dxy <- deldir(xu,yu)
```

*Documentation reproduced from package deldir, version 0.1-9, License: GPL (>= 2)*