# duplicatedxy

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##### 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 internally by 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.

duplicated() deldir()

• duplicatedxy
##### 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)

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