How to limit length of paths in a graph?

I have a graph which looks like this:
Now I want to limit lengths of paths to 2 from node 2, such as this:
So what’s the fastest method?

Limit lengths when doing what operation?
all_simple_paths has a cutoff parameter; set it to 2.
(I would not worry about whether it is “the fastest” method for most applications; generally the underlying implementations in igraph are well tuned.)

Limit lengths when doing what operation?

I want to find some nodes which have limited skips from start in my work codes,so I hope I can get a subgraph which longest path is 2 (or other pointed length),is there a method to change a graph to the form which I want?if not,I will use all_simple_paths to complete this.

I do not understand what you are trying to do. A much clearer, and more detailed explanation would be needed before this can be answered. Include a concrete example.

If you are searching from a specific node (or a set of specific nodes one at a time) you can use igraph::ego, with order = 2, and also set mindist to eliminate the nodes 1 step away.

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Imagine you have a map which contains many train stations and railways,and someone is asking you:“I want to go to stations which are five stations away from here,please give me these stations.”
This is what I want to do.

Dan’s suggestion of ego() accomplishes that.