Line: The line joining two distinct 2D points 'a' and 'b'
In elvanceyhan/pcds: Proximity Catch Digraphs and Their Applications

View source: R/AuxGeometry.R

Line	R Documentation

The line joining two distinct 2D points `a` and `b`

Description

An object of class "Lines". Returns the equation, slope, intercept, and y-coordinates of the line crossing two distinct 2D points a and b with x-coordinates provided in vector x.

This function is different from the line function in the standard stats package in R in the sense that Line(a,b,x) fits the line passing through points a and b and returns various quantities (see below) for this line and x is the x-coordinates of the points we want to find on the Line(a,b,x) while line(a,b) fits the line robustly whose x-coordinates are in a and y-coordinates are in b.

Line(a,b,x) and line(x,Line(A,B,x)$y) would yield the same straight line (i.e., the line with the same coefficients.)

Usage

Line(a, b, x)

Arguments

`a, b`	2D points that determine the straight line (i.e., through which the straight line passes).
`x`	A scalar or a `vector` of scalars representing the `x`-coordinates of the line.

Value

A list with the elements

`desc`	A description of the line
`mtitle`	The `"main"` title for the plot of the line
`points`	The input points `a` and `b` through which the straight line passes (stacked row-wise, i.e., row 1 is point `a` and row 2 is point `b`).
`x`	The input scalar or `vector` which constitutes the `x`-coordinates of the point(s) of interest on the line.
`y`	The output scalar or `vector` which constitutes the `y`-coordinates of the point(s) of interest on the line. If `x` is a scalar, then `y` will be a scalar and if `x` is a `vector` of scalars, then `y` will be a `vector` of scalars.
`slope`	Slope of the line, `Inf` is allowed, passing through points `a` and `b`
`intercept`	Intercept of the line passing through points `a` and `b`
`equation`	Equation of the line passing through points `a` and `b`

Author(s)

Elvan Ceyhan

Examples

## Not run: 
A<-c(-1.22,-2.33); B<-c(2.55,3.75)

xr<-range(A,B);
xf<-(xr[2]-xr[1])*.1
#how far to go at the lower and upper ends in the x-coordinate
x<-seq(xr[1]-xf,xr[2]+xf,l=5)  #try also l=10, 20, or 100

lnAB<-Line(A,B,x)
lnAB
summary(lnAB)
plot(lnAB)

line(A,B)
#this takes vector A as the x points and vector B as the y points and fits the line
#for example, try
x=runif(100); y=x+(runif(100,-.05,.05))
plot(x,y)
line(x,y)

x<-lnAB$x
y<-lnAB$y
Xlim<-range(x,A,B)
if (!is.na(y[1])) {Ylim<-range(y,A,B)} else {Ylim<-range(A,B)}
xd<-Xlim[2]-Xlim[1]
yd<-Ylim[2]-Ylim[1]
pf<-c(xd,-yd)*.025

#plot of the line joining A and B
plot(rbind(A,B),pch=1,xlab="x",ylab="y",
xlim=Xlim+xd*c(-.05,.05),ylim=Ylim+yd*c(-.05,.05))
if (!is.na(y[1])) {lines(x,y,lty=1)} else {abline(v=A[1])}
text(rbind(A+pf,B+pf),c("A","B"))
int<-round(lnAB$intercep,2)  #intercept
sl<-round(lnAB$slope,2)  #slope
text(rbind((A+B)/2+pf*3),ifelse(is.na(int),paste("x=",A[1]),
ifelse(sl==0,paste("y=",int),
ifelse(sl==1,ifelse(sign(int)<0,paste("y=x",int),paste("y=x+",int)),
ifelse(sign(int)<0,paste("y=",sl,"x",int),paste("y=",sl,"x+",int))))))

## End(Not run)

elvanceyhan/pcds documentation built on June 29, 2023, 8:12 a.m.