# Get started

    # 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; built: TRUE; ptr=0x55dcad74ec90>
    #>   graph_class: DAG
    #>   nodes: A, B, C, D
    #>   edges: A-->B, B-->C, B-->D, A-->C

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

#### `ptr`

    cg@ptr
    #> <pointer: 0x55dcad74ec90>

This is the pointer to the Rust object that `caugi` utilizes for performance.

#### `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 graph_builder_add_edges(b, as.integer(unname(id[edges$from])), : Parallel edges not allowed in simple graphs (0 -> 1)

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; built: FALSE; ptr=NULL>
    #>   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 `vignette("performance")` 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

#### `built`

    cg@built
    #> [1] TRUE

This indicates whether the graph has been “built” or not on the Rust side. This is important, as the Rust object may not agree with the R object if `built = FALSE`.

#### `name_index_map`

    cg@name_index_map

The `name_index_map` is a hashmap that takes node names as keys and outputs zero-based indices. This is used to access nodes’ zero-based indices, when converting node names to indices for Rust calls, as the Rust backend uses zero-based indices.

#### `.state`

    cg@.state
    #> <environment: 0x55dcb1322a60>

This is the internal state of the `caugi` graph object. It is used to ensure that the `caugi` object can be modified in R and, so to speak, saves the modifications you might make to the graph in R without having to rebuild the graph in Rust each time. The most important takeaway about the state is that you should avoid modifying the state directly. Instead, you should use the verbs.