Invalid NULL assignment R when having to assign a variable to a shiny app

user_16681187 0
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I see many people running into a similar issue with great answers but I believe this is an unanswered variation to this question!

I have a graph


g <- reactive(graph_from_dataframe(df))

Now I want to assign a degree property to this.


V(g())$degree <- degree(g())

This howevers throws the null assignment error but I don't know how to assign it without calling g. I avoided this by assigning the degree property inside an output$... however this heavily violates DRY and leads to double degree calculation.

shiny igraph r
2 Answers

I guess the following syntax should work

V(g)$degree <- degree(g)
user_121587570

I do not think that reactive(.) objects take assignments.

Two thoughts:

  1. Use reactiveVal:

    g <- reactiveVal()
observeEvent(df, {
  newg <- graph_from_dataframe(df)
  V(newg)$degree <- degree(new)
  g(newg)
})

  2. Handle the $degree assignment in the original reactive:

    g <- reactive({
  newg <- graph_from_dataframe(df)
  V(newg)$degree <- degree(newg)
  newg
})
user_33582720
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