如何解决googleVis::gvisSankey()中的标签重叠问题？

用googleVis::gvisSankey()生成桑基图时，一旦标签长短差异大或者标签过长，很容易出现标签对齐混乱、难以阅读的情况，比如下面的示例代码运行后，短标签（A/B/C）和超长标签混杂，布局严重错位：

library(googleVis) # 0.7.1

dat <- data.frame(From = c("A", "B", "C",
                           "LONG LONG LONG X",
                           "LONG LONG LONG Y",
                           "LONG LONG LONG Z"),
                  To = c("LONG LONG LONG X",
                         "LONG LONG LONG Y",
                         "LONG LONG LONG Z",
                         "LONG LONG LONG 1",
                         "LONG LONG LONG 2",
                         "LONG LONG LONG 3"), 
                  Weight = rep(5, 6))

sk <- gvisSankey(dat, from = "From", to = "To", weight = "Weight")
plot(sk)

下面是几个实用的变通方案：

1. 给长标签手动加换行符拆分 #

把超长标签用\n拆分成多行，让每个标签的整体宽度更均匀，桑基图的节点布局会自动调整，标签就能正常对齐了。修改代码如下：

library(googleVis)

# 给长标签添加换行符
dat$From <- gsub("LONG LONG LONG ", "LONG\nLONG\nLONG ", dat$From)
dat$To <- gsub("LONG LONG LONG ", "LONG\nLONG\nLONG ", dat$To)

sk <- gvisSankey(dat, from = "From", to = "To", weight = "Weight")
plot(sk)

2. 调整Google Charts的配置参数 #

googleVis本质是调用Google Charts的API，我们可以通过options参数传递桑基图的布局配置，比如调整标签的内边距、强制标签换行：

library(googleVis)

sk <- gvisSankey(dat, 
                 from = "From", 
                 to = "To", 
                 weight = "Weight",
                 options = list(
                   sankey = list(
                     node = list(
                       label = list(
                         padding = 15, # 增加标签和节点的间距
                         interpolationThreshold = 0 # 强制所有标签换行，不截断
                       )
                     )
                   )
                 ))
plot(sk)

3. 替换为更灵活的工具包 #

如果上述方法还是达不到预期，可以换成networkD3包的桑基图函数，它对长标签的布局支持更好，自定义空间更大：

library(networkD3)

# 转换数据格式为networkD3要求的结构
links <- dat
names(links) <- c("source", "target", "value")
# 将标签转为索引（networkD3需要数值型的节点索引）
nodes <- data.frame(name = unique(c(links$source, links$target)))
links$source <- match(links$source, nodes$name) - 1
links$target <- match(links$target, nodes$name) - 1

# 生成桑基图
sankeyNetwork(Links = links, Nodes = nodes, 
              Source = "source", Target = "target",
              Value = "value", NodeID = "name",
              fontSize = 12, nodeWidth = 30)

内容的提问来源于stack exchange，提问作者Patrick