R iGraph：如何选择满足特定规则的顶点

这应该是一个简单的问题，但是我真的不知道该怎么做。我有图中的图形：

每个节点都有一个日期，我只想在日期中位数之前的那些节点中找到出度最大的节点。我已经试过了：

library(igraph)
nodes <- data.frame(name=c("a", "c", "d", "e", "f", "g", "i", "j", "k"),
                    date = c(27,   13,  0,   18,  0,   8,   44,  26, 22))
relations <- data.frame(from=c("d", "d", "f", "f","f", "g","g","g","c","c", "e"),
                        to=c("i", "f","d","c","g","k","a","c","a", "e","j"))
ggg <- graph.data.frame(relations, directed=TRUE, vertices=nodes)

V(ggg)$label <- V(ggg)$name
plot(ggg, layout = layout.fruchterman.reingold.grid, edge.curved=FALSE, 
           edge.arrow.size=0.2,edge.arrow.width=0.4)

V(ggg)$label <- V(ggg)$date
plot(ggg, layout = layout.fruchterman.reingold.grid, edge.curved=FALSE, 
     edge.arrow.size=0.2,edge.arrow.width=0.4)

median_delay <- median(V(ggg)$date)
vert_before_median <- V(ggg)[  V(ggg)$date <= median_delay  ]
wnodes <- V(ggg)$name[ degree(ggg,v=vert_before_median,mode="out")==max(degree(ggg,v=vert_before_median,mode="out")) ] 

到目前为止，一切似乎都还可以：

> degree(ggg,v=vert_before_median,mode="out")==max(degree(ggg,v=vert_before_median,mode="out"))
    c     d     e     f     g 
FALSE FALSE FALSE  TRUE  TRUE 

但是，当我想要保留满足此属性的节点时，就会遇到麻烦。我以为wnodes应该包含节点“ f”和“ g”，而不是

> wnodes
[1] "e" "f" "k"

看来我在尝试从图中选择顶点的方式上缺少某些东西。我已经尝试过which，但仍然不正确：

> V(ggg)[which( degree(ggg,v=vert_before_median,mode="out")==max(degree(ggg,v=vert_before_median,mode="out"))   )]
Vertex sequence:
[1] "e" "f"

任何想法？