ABCxy {plothelper}

Symmetrical Transformation

Description

A1 and A2 are symmetrical on the two sides of Ax+By+C=0. The input of the function is A1, and the result is A2. The function also works when the line is horizontal or vertical. Note: the two shapes are symmetrical only when ggplot2::coord_fixed() is used.

Usage

ABCxy(
  x,
  A,
  B,
  C,
  p1 = NULL,
  p2 = NULL,
  f = NULL,
  group = TRUE,
  todf = TRUE,
  checks = TRUE
)

Arguments

x

the input. It can be a data frame, matrix, tibble object, or a list of these kinds of objects. Each object must have exactly 2 columns and must be numeric without NA. If it has more than 2 columns, only the first 2 columns will be used.

A

for Ax+By+C=0.

B

for Ax+By+C=0.

C

for Ax+By+C=0.

p1

if A, B, C are not given, you can also give two points p1 and p2 on the supposed Ax+By+C=0 line. Note: if A, B, C, p1, p2 are all given, the given A, B, C will be ignored. It must be a vector of length 2. The first element is x and the second is y.

p2

see p1.

f

argument passed to split to divide a data frame into a list of data frames. It should be a vector whose length is equal to the number of rows of x (if x is a data frame).

group

default is TRUE. It indicates whether to add a 3rd column named "g" to label the group number of each group of points. It is useful when using aes(...group=g) with 'ggplot2'.

todf

default is TRUE. It indicates whether to combine the output (a list) into a data frame.

checks

default is TRUE. It indicates whether to check input validity. Do not turn it off unless you are sure that the input is OK.

Value

if todf = TRUE, the output will be a data frame with coordinates of possibly several polygons, otherwise, it will be a list of data frames. Data frames have 2 columns named "x" and "y", and if group = TRUE, a third column named "g" is added indicating group numbers.

Examples

library(ggplot2)
dat1=data.frame(x=c(0, 2, 2, 0), y=c(0, 0, 1, 1))
dat2=ABCxy(dat1, -1, -1, 3)
ggplot()+
	coord_fixed()+
	geom_polygon(data=dat1, aes(x=x, y=y), fill="red")+
	geom_polygon(data=dat2, aes(x=x, y=y), fill="blue")+
	geom_abline(intercept=3, slope=-1)		
dat3=ABCxy(dat1, p1=c(0, 1), p2=c(-0.5, 0), todf=TRUE)
ggplot()+
	coord_fixed()+
	geom_polygon(data=dat1, aes(x=x, y=y), fill="red")+
	geom_polygon(data=dat3, aes(x=x, y=y), fill="blue")+
	geom_abline(intercept=1, slope=2)