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Give the Quadrant Number of Planar Points

quadrant.Rd

Determine the quadrant of planar points, i.e. in which of the four parts cut by the x- and y- axis the points lie. Zero values (i.e. points on the axes) are treated as if positive.

Usage

quadrant(x, y=NULL)

Arguments

x,y

numeric vectors of the same length, or x is an \(x-y\) structure and y=NULL, see xy.coords.

Value

numeric vector of same length as x (if that's a vector) with values in 1:4 indicating the quadrant number of the corresponding point.

Examples

xy <- as.matrix(expand.grid(x= -7:7, y= -7:7)); rownames(xy) <- NULL
(qu <- quadrant(xy))
#>   [1] 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 3 3 3 3 3 3 3
#>  [38] 4 4 4 4 4 4 4 4 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 3 3 3 3 3 3 3 4 4 4 4 4 4 4
#>  [75] 4 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 2 2 2 2 2 2
#> [112] 2 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 1 1 1 1 1 1
#> [149] 1 1 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 2 2 2 2 2
#> [186] 2 2 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 1 1 1 1 1
#> [223] 1 1 1
plot(xy, col = qu+1, main = "quadrant() number", axes = FALSE)
abline(h=0, v=0, col="gray") # the x- and y- axis
text(xy, lab = qu, col = qu+1, adj = c(1.4,0))