# caugi

    # load the package
    library(caugi)

In this vignette, we will walk you through how to create a `caugi`, query it, modify it, and then compare it to other `caugi`s.

## The `caugi` object

You can create a `caugi` graph object using the `caugi()` function along with infix operators to define edges. Let’s create a directed acyclic graph (DAG) with 5 nodes and 5 edges.

    cg <- caugi(
      A %-->% B %-->% C + D,
      A %-->% C,
      class = "DAG"
    )
    cg
    #> <caugi object; 4 nodes, 4 edges; simple: TRUE; session=0x556548d4a760>
    #>   graph_class: DAG
    #>   nodes: A, B, C, D
    #>   edges: A-->B, A-->C, B-->C, B-->D

You might scratch your head a bit, when looking at the call above. To clarify, `A %-->% B` creates the edge `-->` from `A` to `B`. The syntax `B %-->% C + D` is equivalent to `B %-->% C` and `B %-->% D`. Notice that the graph prints two `tibbles`. The first is equivalent to `cg@nodes` and the second `cg@edges`. Besides that, the `caugi` holds other properties. Let’s check the other properties.

### Properties

#### `session`

    cg@session
    #> <pointer: 0x556548d4a760>

This is the session pointer to the Rust graph object that `caugi` utilizes for performance. The session manages lazy compilation and caching of graph operations internally.

#### `simple`

    cg@simple
    #> [1] TRUE

This indicates whether the graph is simple or not. Let’s try to create a non-simple graph:

    caugi(A %-->% B, B %-->% A)
    #> Error in rs_resolve_class(session, class): Parallel edges not allowed in simple graphs (A -> B)

This cannot be done unless you initialize the graph with `simple = FALSE`. Note that, currently, all of the supported graph classes only support `simple = TRUE` unless the class is `UNKNOWN`.

#### `graph_class`

    cg@graph_class
    #> [1] "DAG"

This is the graph’s class. As you can see here, it is a DAG.

## Querying the `caugi`

We can query the `caugi` graph object with the built-in queries provided in the package. Let’s try to find the descendants of all the parents of the node `C`:

    descendants(cg, parents(cg, "C"))
    #> $A
    #> [1] "B" "C" "D"
    #>
    #> $B
    #> [1] "C" "D"

First note that the output is a list of named character vectors. How come? Since the parents of `C` is `c(A, B)`:

    parents(cg, "C")
    #> [1] "A" "B"

So for each parent of `C` we have a named vector in the list that represents the descendants of that parent node.

## Modifying the `caugi`

Let’s try to modify the graph from before, so we get a new DAG.

    cg_modified <- cg |>
      remove_edges(A %-->% B, B %-->% C + D) |>
      add_edges(B %-->% A, D %-->% C)
    cg_modified
    #> <caugi object; 4 nodes, 3 edges; simple: TRUE; session=0x5565456998c0>
    #>   graph_class: DAG
    #>   nodes: A, B, C, D
    #>   edges: A-->C, B-->A, D-->C

Would you like to add nodes? Then use `add_nodes()`.

## Graph metrics

Now that we have two different graphs, we can use different metrics to measure the difference between the two graphs. Here, we use the adjustment identification distance (AID) and the structural Hamming distance (SHD):

    aid(cg, cg_modified)
    #> [1] 0.5833333
    shd(cg, cg_modified, normalized = TRUE)
    #> [1] 0.6666667

## There you go!

You have now created a graph, inspected it, modified it, and measured the difference between the two graphs – both structurally and interventionally.

For further reading, we recommend the vignettes `vignette("package_use")` and performance article on our website to see how to use `caugi` in your own packages, and to see how `caugi` performs compared to other graph packages in R. For the interested reader, we also recommend `vignette("motivation")`, which goes deeper into the motivation behind `caugi` and what we aspire to do with `caugi`.

## Appendix

### Advanced properties

#### `name_index_map`

#### `session`

    cg@session
    #> <pointer: 0x556548d4a760>

This is the Rust GraphSession pointer that holds the canonical graph state. The session handles lazy compilation and caching of graph operations internally. You should avoid accessing or modifying the session directly. Instead, use the provided accessor properties (`@nodes`, `@edges`, `@simple`, `@graph_class`) and verb functions (`add_edges()`, `remove_nodes()`, etc.).