Annotate graph vertices fails

Question

According to the docs this should work but for some reason does not:

g = CompleteGraph[3];
Annotate[{g, 3}, "a" -> 17];
AnnotationValue[{g, 3}, "a"]

It returns $Failed, both on desktop and in the cloud. On the other hand, if one uses

AnnotationValue[{g, 3}, "a"] = 17

the annotation does works. A glitch in paradise?

Szabolcs · Accepted Answer · 2020-04-01 09:26:55Z

1

This is not a bug.

Annotate does not modify the graph. Instead, it returns a new graph. It is like Append and not like AppendTo.

g = CompleteGraph[3];
g2 = Annotate[{g, 3}, "a" -> 17];
AnnotationValue[{g2, 3}, "a"]

answered Apr 1, 2020 at 9:26

Szabolcs

236k31 gold badges641 silver badges1.3k bronze badges

$\begingroup$ Ah! Each and every (incremental) annotation creates a new graph. Not what 'annotation' typically means and a waste of memory as well, but what can one do. $\endgroup$
– Francois Vanderseypen
Commented Apr 1, 2020 at 9:31
$\begingroup$ @FrancoisVanderseypen "but what can one do" One of two things: (1) your approach with AnnotationValue[...] = ... (2) Set multiple properties at the same time. E.g., do not set it vertex by vertex. Set it at once for all vertices. Both will improve performance significantly. $\endgroup$
– Szabolcs
Commented Apr 1, 2020 at 11:10
1

$\begingroup$ @FrancoisVanderseypen Also, do check out my IGraph/M package which makes some operations on properties easier, and carefully avoids badly performing constructs (when possible). szhorvat.net/mathematica/IGDocumentation/… $\endgroup$
– Szabolcs
Commented Apr 1, 2020 at 11:11

Add a comment |

1 Answer 1