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Returning the argument of a function if the argument is not of the right type

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2

$begingroup$

Best to give an example. Let us consider the function AdjacencyMatrix. When we pass, say a matrix to it, we get:

test = 1,1,1,1,2,2,3,3,3;
AdjacencyMatrix[%]

AdjacencyMatrix::graph: A graph object is expected at position 1 in AdjacencyMatrix[1,1,1,1,2,2,3,3,3].

AdjacencyMatrix[1, 1, 1, 1, 2, 2, 3, 3, 3]

Is there a way of modifying AdjacencyMatrix so that if the argument isn't a graph object it would simply return the argument itself?

functions attributes

share|improve this question

asked 8 hours ago

amator2357amator2357

8121010 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  You want AdjacencyMatrix to return the argument itself only when it is a matrix, or whenever it is not a graph?
  $endgroup$
  – AccidentalFourierTransform
  7 hours ago
  

  
  
  
  

add a comment | 

2

$begingroup$

Best to give an example. Let us consider the function AdjacencyMatrix. When we pass, say a matrix to it, we get:

test = 1,1,1,1,2,2,3,3,3;
AdjacencyMatrix[%]

AdjacencyMatrix::graph: A graph object is expected at position 1 in AdjacencyMatrix[1,1,1,1,2,2,3,3,3].

AdjacencyMatrix[1, 1, 1, 1, 2, 2, 3, 3, 3]

Is there a way of modifying AdjacencyMatrix so that if the argument isn't a graph object it would simply return the argument itself?

functions attributes

share|improve this question

asked 8 hours ago

amator2357amator2357

8121010 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  You want AdjacencyMatrix to return the argument itself only when it is a matrix, or whenever it is not a graph?
  $endgroup$
  – AccidentalFourierTransform
  7 hours ago
  

  
  
  
  

add a comment | 

$begingroup$

Best to give an example. Let us consider the function AdjacencyMatrix. When we pass, say a matrix to it, we get:

test = 1,1,1,1,2,2,3,3,3;
AdjacencyMatrix[%]

AdjacencyMatrix::graph: A graph object is expected at position 1 in AdjacencyMatrix[1,1,1,1,2,2,3,3,3].

AdjacencyMatrix[1, 1, 1, 1, 2, 2, 3, 3, 3]

Is there a way of modifying AdjacencyMatrix so that if the argument isn't a graph object it would simply return the argument itself?

functions attributes

share|improve this question

asked 8 hours ago

amator2357amator2357

8121010 bronze badges

$endgroup$

test = 1,1,1,1,2,2,3,3,3;
AdjacencyMatrix[%]

share|improve this question

asked 8 hours ago

amator2357amator2357

8121010 bronze badges

share|improve this question

asked 8 hours ago

amator2357amator2357

8121010 bronze badges

asked 8 hours ago

amator2357amator2357

8121010 bronze badges

asked 8 hours ago

amator2357amator2357

8121010 bronze badges

2 Answers
2

active

oldest

votes

3

$begingroup$

You can use Check in a user defined function:

adjacencyMatrix[g_] := Check[AdjacencyMatrix[g], g]

Then:

adjacencyMatrix[Graph[1->2,2->3,3->4]] //Normal
adjacencyMatrix[1->2, 2->3, 3->4] //Normal
adjacencyMatrix[1,2,3,4]

0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0

0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0

AdjacencyMatrix::graph: A graph object is expected at position 1 in AdjacencyMatrix[1,2,3,4].

1, 2, 3, 4

share|improve this answer

answered 7 hours ago

Carl WollCarl Woll

86.8k33 gold badges114114 silver badges221221 bronze badges

$endgroup$

add a comment | 

4

$begingroup$

Bad answer:

Unprotect[AdjacencyMatrix];
AdjacencyMatrix[mat_List] := mat
Protect[AdjacencyMatrix];

Good answer:

adjacencyMatrix[graph_Graph] := AdjacencyMatrix[graph]
adjacencyMatrix[mat_List] := mat

share|improve this answer

answered 8 hours ago

AccidentalFourierTransformAccidentalFourierTransform

6,29711 gold badge1212 silver badges4545 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  For the good answer, maybe remove the pattern head List on the second line, as this is the behavior requested for anything that's not a Graph.
  $endgroup$
  – Roman
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @Roman good point. Let me ask OP to be sure. (If they only want the identity for matrices, then it is safer to leave List in).
  $endgroup$
  – AccidentalFourierTransform
  7 hours ago
  

  
  
  
  

add a comment | 

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3

$begingroup$

You can use Check in a user defined function:

adjacencyMatrix[g_] := Check[AdjacencyMatrix[g], g]

Then:

adjacencyMatrix[Graph[1->2,2->3,3->4]] //Normal
adjacencyMatrix[1->2, 2->3, 3->4] //Normal
adjacencyMatrix[1,2,3,4]

0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0

0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0

AdjacencyMatrix::graph: A graph object is expected at position 1 in AdjacencyMatrix[1,2,3,4].

1, 2, 3, 4

share|improve this answer

answered 7 hours ago

Carl WollCarl Woll

86.8k33 gold badges114114 silver badges221221 bronze badges

$endgroup$

add a comment | 

3

$begingroup$

You can use Check in a user defined function:

adjacencyMatrix[g_] := Check[AdjacencyMatrix[g], g]

Then:

adjacencyMatrix[Graph[1->2,2->3,3->4]] //Normal
adjacencyMatrix[1->2, 2->3, 3->4] //Normal
adjacencyMatrix[1,2,3,4]

0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0

0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0

AdjacencyMatrix::graph: A graph object is expected at position 1 in AdjacencyMatrix[1,2,3,4].

1, 2, 3, 4

share|improve this answer

answered 7 hours ago

Carl WollCarl Woll

86.8k33 gold badges114114 silver badges221221 bronze badges

$endgroup$

add a comment | 

$begingroup$

You can use Check in a user defined function:

adjacencyMatrix[g_] := Check[AdjacencyMatrix[g], g]

Then:

adjacencyMatrix[Graph[1->2,2->3,3->4]] //Normal
adjacencyMatrix[1->2, 2->3, 3->4] //Normal
adjacencyMatrix[1,2,3,4]

0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0

0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0

AdjacencyMatrix::graph: A graph object is expected at position 1 in AdjacencyMatrix[1,2,3,4].

1, 2, 3, 4

share|improve this answer

answered 7 hours ago

Carl WollCarl Woll

86.8k33 gold badges114114 silver badges221221 bronze badges

$endgroup$

adjacencyMatrix[g_] := Check[AdjacencyMatrix[g], g]

adjacencyMatrix[Graph[1->2,2->3,3->4]] //Normal
adjacencyMatrix[1->2, 2->3, 3->4] //Normal
adjacencyMatrix[1,2,3,4]

share|improve this answer

answered 7 hours ago

Carl WollCarl Woll

86.8k33 gold badges114114 silver badges221221 bronze badges

answered 7 hours ago

Carl WollCarl Woll

86.8k33 gold badges114114 silver badges221221 bronze badges

answered 7 hours ago

Carl WollCarl Woll

86.8k33 gold badges114114 silver badges221221 bronze badges

4

$begingroup$

Bad answer:

Unprotect[AdjacencyMatrix];
AdjacencyMatrix[mat_List] := mat
Protect[AdjacencyMatrix];

Good answer:

adjacencyMatrix[graph_Graph] := AdjacencyMatrix[graph]
adjacencyMatrix[mat_List] := mat

share|improve this answer

answered 8 hours ago

AccidentalFourierTransformAccidentalFourierTransform

6,29711 gold badge1212 silver badges4545 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  For the good answer, maybe remove the pattern head List on the second line, as this is the behavior requested for anything that's not a Graph.
  $endgroup$
  – Roman
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @Roman good point. Let me ask OP to be sure. (If they only want the identity for matrices, then it is safer to leave List in).
  $endgroup$
  – AccidentalFourierTransform
  7 hours ago
  

  
  
  
  

add a comment | 

4

$begingroup$

Bad answer:

Unprotect[AdjacencyMatrix];
AdjacencyMatrix[mat_List] := mat
Protect[AdjacencyMatrix];

Good answer:

adjacencyMatrix[graph_Graph] := AdjacencyMatrix[graph]
adjacencyMatrix[mat_List] := mat

share|improve this answer

answered 8 hours ago

AccidentalFourierTransformAccidentalFourierTransform

6,29711 gold badge1212 silver badges4545 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  For the good answer, maybe remove the pattern head List on the second line, as this is the behavior requested for anything that's not a Graph.
  $endgroup$
  – Roman
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @Roman good point. Let me ask OP to be sure. (If they only want the identity for matrices, then it is safer to leave List in).
  $endgroup$
  – AccidentalFourierTransform
  7 hours ago
  

  
  
  
  

add a comment | 

$begingroup$

Bad answer:

Unprotect[AdjacencyMatrix];
AdjacencyMatrix[mat_List] := mat
Protect[AdjacencyMatrix];

Good answer:

adjacencyMatrix[graph_Graph] := AdjacencyMatrix[graph]
adjacencyMatrix[mat_List] := mat

share|improve this answer

answered 8 hours ago

AccidentalFourierTransformAccidentalFourierTransform

6,29711 gold badge1212 silver badges4545 bronze badges

$endgroup$

Unprotect[AdjacencyMatrix];
AdjacencyMatrix[mat_List] := mat
Protect[AdjacencyMatrix];

adjacencyMatrix[graph_Graph] := AdjacencyMatrix[graph]
adjacencyMatrix[mat_List] := mat

share|improve this answer

answered 8 hours ago

AccidentalFourierTransformAccidentalFourierTransform

6,29711 gold badge1212 silver badges4545 bronze badges

answered 8 hours ago

AccidentalFourierTransformAccidentalFourierTransform

6,29711 gold badge1212 silver badges4545 bronze badges

answered 8 hours ago

AccidentalFourierTransformAccidentalFourierTransform

6,29711 gold badge1212 silver badges4545 bronze badges