Question

I have a graph g which contains a bunch of nodes/vertexes, which are connected by edges, each of the edges has a particular numeric attribute value. An edge list might look like:

v1 v2 att
a b 17
a c 6
a d 2
b c 9

For visualisation purposes I need to add the highest and lowest att numbers connected to each vertex (coming or going; direction doesn't matter here).

So for example I'd like to set v$max for a to 17 and v$min for a to 2, because the largest att-value of a link connected to a is 17, and the smallest is 2.

I tried some variants along the theme of this:

V(g)$min=min(E(g)[incident(g,V(g), mode='total')]$att)

This seems to be very nearly right in that it appears to give the right answer when I try it on a single node, as in

min(E(g)[incident(g,V(g)[2], mode='total')]$att)

but it doesn't work when I try it across all nodes. The aim is to get V(g)$min and V(g)$max set for every vertex.

Answer 1

希望这不是一个家庭作业问题，你只是错过了概括部分

library(igraph)
library(plyr)
df <- data.frame(read.table(text="v1 v2 weight
a b 17
a c 6
a d 2
b c 9", header=T))
df$weight <- as.numeric(df$weight)

#transform df into igraph
g <- graph.data.frame(df, directed=F, vertices=NULL)    

#for each vertex, get all incidental edges, weights and use range to find min & max
ldply(V(g), function(v) range(incident(g, v, mode='total')$weight))

Using IGraph in R, how to calculate highest/lowest edge attribute value from those connected to each vertex?

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