按比例为图表上的点着色

Question

我在 R 中有这张图：

library(igraph)

width <- 30
height <- 20
num_nodes <- width * height

x <- rep(1:width, each = height)
y <- rep(1:height, times = width)

g <- make_empty_graph(n = num_nodes, directed = FALSE)

get_node_index <- function(i, j) (i - 1) * height + j

edges <- c()
for(i in 1:width) {
    for(j in 1:height) {
        current_node <- get_node_index(i, j)
        
        if(i < width) edges <- c(edges, current_node, get_node_index(i + 1, j))
        
        if(j < height) edges <- c(edges, current_node, get_node_index(i, j + 1))
    }
}

g <- add_edges(g, edges)

V(g)$x <- x
V(g)$y <- y

par(mfrow=c(1,1))

V(g)$name <- 1:num_nodes
plot(g, vertex.size = 7, vertex.label = V(g)$name, vertex.label.cex = 0.6, main = "Map with         Node Indices")

我想在该图上选择一些节点，并根据它们距该节点的距离成比例地为该图上的所有节点着色。也就是说，相同距离的所有节点都具有相同的颜色 - 距离该节点较近的节点颜色较深，而距离较远的节点颜色较浅。

根据我之前的问题（计算图表上多个点之间的最短距离？），我尝试这样做（例如选择节点 50）：

distances_from_50 <- distances(g, v = 50, to = V(g))
max_dist <- max(distances_from_50)

color_palette <- colorRampPalette(c("#08306B", "#F7FBFF"))(max_dist + 1)

V(g)$color <- color_palette[distances_from_50 + 1]

V(g)$color[50] <- "red"

par(mfrow=c(1,1), mar=c(5,4,4,2))
plot(g, 
     vertex.size = 7,
     vertex.label = V(g)$value,
     vertex.label.cex = 0.6,
     main = "Distance-based Color Gradient from Node 50",
     layout = cbind(V(g)$x, V(g)$y))

还有其他办法可以让颜色较深的节点仍然具有可见的标签吗？

Answer 1

我认为这取决于您对颜色区分的主观看法。您可以专门为顶点标签定义调色板，例如，

labelcolor_palette <- colorRampPalette(c("white", "lightyellow", "red", "purple", "black"))(max_dist + 1)
V(g)$labelcolor <- labelcolor_palette[distances_from_50 + 1]
plot(g,
    vertex.size = 7,
    vertex.label = V(g)$value,
    vertex.label.cex = 1,
    vertex.label.color = V(g)$labelcolor,
    main = "Distance-based Color Gradient from Node 50",
    layout = cbind(V(g)$x, V(g)$y)
)