I used r and igraph 1.3.0 verson to analysis my data, the problem is show below, but I don‘t know why it is happened, can someone help to solve this problem? thanks.
Please always show a complete minimal example, otherwise it is very hard to tell what happened.
A possible cause is that you requested a smaller number of clusters than the number of connected components.
I now see that the R interface does not provide an explicit way to request a certain number of clusters with walktrap. Please show a complete minimal example so that we can reproduce the problem.
FYI, I found a small reproducer: Walktrap community detection fails on some disconnected weighted graphs · Issue #2042 · igraph/igraph · GitHub
Got it, thanks, hope it can solve my problem.