在ggplot2中绘制一系列填充六边形

Question

我正在尝试在 ggplot2 中创建填充六边形（以六边形格子为中心的多边形）的镶嵌。我已经使用“plot”命令完成了这项工作，但正在努力将其转换为 ggplot。

这是设置的代码：

# Generate a lattice of points equally spaced in the centers of a hexagonal lattice
dist = 1     # distance between the centers of hexagons
nx = dist*15 # horizontal extent
ny = dist*15 # vertical extent      

MakeHexLattice = function(nx, ny, dist, origin=c(0,0)) {
  locations = cbind(location = 1:(nx*ny),
                    x = sort(c(rep(seq(from=0, by=dist, length.out=nx),each=ceiling(ny/2)),
                               rep(seq(from=dist/2, by=dist, length.out=nx),
                                   each=floor(ny/2)))) + origin[1],
                    y = rep(c(seq(from=0, by = dist*sqrt(3), length.out=ceiling(ny/2)),
                              seq(from=dist*sqrt(3)/2, by=dist*sqrt(3),
                                  length.out=floor(ny/2))) + origin[2], times=nx))
  class(locations) = c(class(locations), "lattice")
  attr(locations, "gridsize") = dist
  return(locations)
}

下面是使用'plot'创建图像的代码，看起来很不错：

landscape = MakeHexLattice(nx=nx,ny=ny,dist=dist,origin=c(0,0))

# Plot hexagonal lattice as points
plot(x=landscape[,2],y=landscape[,3], pch=19, col="black", cex=0.5, asp=1/1)

# Separate x and y coordinates
lx = landscape[,2] # x-coordinates
ly = landscape[,3] # y-coordinates      

# Plot hexagonal lattice as filled hexagons
hex.x = cbind(lx + 0, lx + 0.5, lx + 0.5, lx + 0, lx - 0.5, lx - 0.5) 
hex.y = cbind(ly - 1/(sqrt(3)), ly - 1/(2*sqrt(3)), ly + 1/(2*sqrt(3)), ly + 1/(sqrt(3)), ly + 1/(2*sqrt(3)), ly - 1/(2*sqrt(3)))
hex.vectors = cbind(hex.x, hex.y)

for(i in 1:(length(hex.vectors)/12)){
  polygon(x=hex.vectors[i,1:6], y=hex.vectors[i,7:12], angle = 120, border=NULL, col="wheat", 
          lty = par("lty"), fillOddEven = FALSE)
}

关于如何使用 ggplot2（我正在过渡到使用）来完成同样的事情的任何提示？我曾尝试使用 geom_polygon 但似乎无法解决 for 循环。 （另外，请不要告诉我使用 'hexbin' -- 这不是我想要实现的目标！）

感谢您的帮助！

Answer 1

与 ggplot 中的大多数东西一样，绘图实际上非常简单，大部分工作是让您的数据具有正确的形状，以使其有意义。 for 循环是完全没有必要的，geom_polygon() 只需要一个带有 x 和 y 坐标的数据框，以及一个定义它们所属组的变量。使用您的数据：

library(ggplot2)
library(reshape2)

#Get your coordinates in long format with an id
hexdat.x <- melt(cbind(id = 1:length(hex.x), as.data.frame(hex.x)), id.vars = "id", value.name = "x")
hexdat.y <- melt(cbind(id = 1:length(hex.y), as.data.frame(hex.y)), id.vars = "id", value.name = "y")

#Merge them into the same dataframe
hexdat <- merge(hexdat.x, hexdat.y)

head(hexdat)
#   id variable    x          y
# 1  1       V1  0.0 -0.5773503
# 2  1       V2  0.5 -0.2886751
# 3  1       V3  0.5  0.2886751
# 4  1       V4  0.0  0.5773503
# 5  1       V5 -0.5  0.2886751
# 6  1       V6 -0.5 -0.2886751

现在要绘制六边形，您只需给ggplot x 和 y 坐标，并指定每个六边形所属的组：

ggplot(hexdat, aes(x, y)) + 
  geom_polygon(aes(group = id), fill = "wheat", colour = "black")