Converting Association to Matrix

Question

Imagine I have the following association, where the keys are given as pairs of natural numbers

assoc = <|{1, 1} -> 0, {2, 1} -> 1, {1, 3} -> 0, {3, 2} -> 0, {1, 2} -> 1, {3, 1} -> 0,
    {2, 3} -> 0, {3, 3} -> 1, {2, 2} -> 0|>

To get the connectivity matrix defined by this association, where in {i, j}, i is the row and j is the column, I can do

Partition[Values@KeySort@assoc, 3]
Out[]= {{0, 1, 0}, {1, 0, 0}, {0, 0, 1}}

Is there a faster way to directly get the previous matrix (or list of lists)?

Try SparseArray[Normal[assoc]] or (if you know the dimensions in advance) SparseArray[Normal[assoc],{3,3}]. — Henrik Schumacher, Commented Sep 17, 2021 at 19:45
Thinking of it, SparseArray[Keys[assoc] -> Values[assoc], {3, 3}] should perform better for long assiciations. — Henrik Schumacher, Commented Sep 17, 2021 at 19:47

Alan · Accepted Answer · 2021-09-18 20:42:48Z

1

nodes = Union@Catenate@Keys@assoc
edges = Cases[Normal@assoc, ({x_, y_} -> 1) :> x -> y]
AdjacencyMatrix@Graph[nodes, edges]  (* a SparseArray *)

answered Sep 17, 2021 at 20:48

Alan

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