stretchxy {plothelper}

Stretching Transformation

Description

A2 (output) is the result of enlarging (or shrinking) A1 (input) in x dimension and y dimension. Note: the two shapes manifest enlarging or shrinking effect only when ggplot2::coord_fixed() is used.

Usage

stretchxy(
  x,
  xlarge = 2,
  ylarge = 2,
  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.

xlarge

the enlarging extent in x dimension. If it is smaller than 1, the shape will be shrinking.

ylarge

the enlarging extent in y dimension. If it is smaller than 1, the shape will be shrinking.

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, 1, 1), y=c(0, 0, 1))
dat2=data.frame(x=c(4, 5, 5, 4), y=c(0, 0, 3, 3))
dat3=stretchxy(list(dat1, dat2), xlarge=3, ylarge=c(3, 2), todf=TRUE)
ggplot()+coord_fixed()+
	geom_polygon(data=dat1, aes(x, y), fill="red", alpha=0.3)+
	geom_polygon(data=dat2, aes(x, y), fill="blue", alpha=0.3)+
	geom_polygon(data=dat3, aes(x, y, fill=g, group=g), fill="blue", alpha=0.3)