CODEWITHSUNDEEP
haskellgraphviz
mjarosie
mjarosie

Reputation: 4593

How to plot graph labels with Haskell's graphviz package

This question does not solve the problem that I'm facing, but my question is based on it.

What I'm trying to achieve is to plot a directed graph with labelled nodes and unlabelled edges using graphviz package. In my case nodes have labels of type String (the type definition of the graph is Gr String ()). Here's the code (where used graph is a minified version of clr486 - a perfect example of my use case):

module Main where

import              Data.Graph.Inductive.Graph          (mkGraph)
import              Data.Graph.Inductive.PatriciaTree   (Gr)
import              Data.GraphViz                       (graphToDot, nonClusteredParams)
import              Data.GraphViz.Printing              (renderDot, toDot)
import              Data.Text.Lazy                      (unpack)

main :: IO ()
main = do
    let exampleGraph = mkGraph (zip [1..3] ["shorts", "socks", "watch"]) [(1,2,()),(2,3,())] :: Gr String ()
    putStrLn $ unpack $ renderDot $ toDot $ graphToDot nonClusteredParams exampleGraph

It looks like the "labels" in context of graphviz haskell package don't mean what I'd assume are the actual labels of the graph - the resulting graph's labels turn out to be its "internal" indices. The output of this code is:

digraph {
    1;
    2;
    3;
    1 -> 2;
    2 -> 3;
}

And when passed to dot resulting graph looks like this:

resulting graph

But what I'd like to achieve is the following:

expected result

Upvotes: 2

Views: 296

Answers (1)

Bjartur Thorlacius
Bjartur Thorlacius

Reputation: 804

Try customizing your parameters. Something along these lines might work:

module Main where

import              Data.Functor                        ((<&>))
import qualified    Data.Text.Lazy as L                 (pack)
import qualified    Data.Text.Lazy.IO as IO             (putStrLn)
import              Data.Graph.Inductive.Graph          (mkGraph)
import              Data.Graph.Inductive.PatriciaTree   (Gr)
import              Data.GraphViz                       (graphToDot, nonClusteredParams, fmtNode)
import              Data.GraphViz.Attributes.Complete   (Label(StrLabel), Attribute(Label))
import              Data.GraphViz.Printing              (renderDot, toDot)

exampleGraph :: Gr String ()
exampleGraph = mkGraph (zip [1..3] ["shorts", "socks", "watch"]) [(1,2,()),(2,3,())]

labelledNodesParams = nonClusteredParams { fmtNode= \(_,label)-> [Label (StrLabel (L.pack label))] }

putGraph :: Gr String () -> IO ()
putGraph = graphToDot labelledNodesParams <&> toDot <&> renderDot <&> IO.putStrLn

main = putGraph exampleGraph

Upvotes: 3

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