get_attr: Get and Set Nodal Attributes in Network Models
In EpiModel: Mathematical Modeling of Infectious Disease Dynamics

get_attr

R Documentation

Get and Set Nodal Attributes in Network Models

Description

Retrieve, create, and edit the nodal attributes of the main netsim_dat object of network models, from inside module functions. Each nodal attribute is a vector with one value per node, indexed by the positional identifiers of the nodes (posit_ids).

get_attr() returns one attribute, for all nodes or for the nodes in posit_ids. get_attr_list() returns several attributes as a named list.
set_attr() replaces the values of an attribute, for all nodes or for the nodes in posit_ids, and creates the attribute if it does not exist. add_attr() creates an attribute set to NA for all nodes.
append_core_attr() adds n.new nodes and sets their core attributes. append_attr() then adds the values of each other attribute for the same nodes.
remove_node_attr() removes the nodes in posit_ids from every attribute.
get_core_attributes() lists the core attributes with their types.

See net-accessor for an overview of the accessors.

Usage

get_attr(dat, item, posit_ids = NULL, override.null.error = FALSE)

get_attr_list(dat, item = NULL)

set_attr(dat, item, value, posit_ids = NULL, override.length.check = FALSE)

add_attr(dat, item)

append_attr(dat, item, value, n.new)

append_core_attr(dat, at, n.new)

remove_node_attr(dat, posit_ids)

get_core_attributes()

Arguments

`dat`	Main `netsim_dat` object containing a `networkDynamic` object and other initialization information passed from `netsim()`.
`item`	Name of the nodal attribute. For `get_attr_list()`, a character vector of names, or `NULL` (default) for all attributes.
`posit_ids`	Positional identifiers of the nodes. For `get_attr()` and `set_attr()`, the nodes to get or edit, with `NULL` (default) for all nodes; for `remove_node_attr()`, the nodes to remove.
`override.null.error`	If `TRUE`, return `NULL` instead of an error when `item` does not exist (default = `FALSE`).
`value`	New values of the attribute. For `set_attr()`, one value per node, or with `posit_ids`, one value per selected node or a single value for all of them. For `append_attr()`, one value per new node or a single value for all of them.
`override.length.check`	If `TRUE`, `set_attr()` accepts a `value` whose length differs from the number of nodes (default = `FALSE`). Every attribute must again hold one value per node by the end of the time step.
`n.new`	Number of new nodes: for `append_core_attr()`, the nodes to add; for `append_attr()`, the number of values to append at the end of `item`.
`at`	Current time step, recorded as the entry time (`entrTime`) of the new nodes.

Value

For get_attr(), the attribute vector, or its values for the nodes in posit_ids; for get_attr_list(), a named list of attribute vectors; for get_core_attributes(), a named list with a value of the correct type for each core attribute. The other functions return the updated netsim_dat object.

Core Attributes

The append_core_attr function initializes the attributes necessary for EpiModel to work (the four core attributes are: "active", "unique_id", "entrTime", and "exitTime"). These attributes are used in the initialization phase of the simulation, to create the nodes (see initialize.net()); and also used when adding nodes during the simulation (see arrivals.net()).

One Value Per Node

Every nodal attribute holds exactly one value per node, and netsim() checks this at the end of each time step. When set_attr and append_attr create an attribute, the nodes they do not write to are filled with NA to preserve that: set_attr with posit_ids fills the unselected nodes, and append_attr fills the nodes that predate the ones being appended. This means append_core_attr must be called before append_attr when adding new nodes, as it is what makes those nodes known to the rest of the object.

Intended Usage

These accessors operate on the live netsim_dat object that EpiModel constructs internally when a simulation starts and passes through each module at every time step. The expected calling context is inside a user-supplied module function (e.g., a custom infection.FUN, recovery.FUN, or arrivals/departures module) registered with control.net().

They are not a general-purpose tool for editing the user-facing input or output objects of netsim():

Calling them on a param.net(), init.net(), or control.net() object before a run will appear to succeed (those objects are also list-like) but produces an object that is not a valid simulation input.
Calling them on the object returned by netsim() modifies only the saved input slot, not anything that would change the result of a re-run. Note also that netsim() strips the ⁠*.FUN⁠ entries from its returned control slot, so feeding that slot back into a new simulation will fail.

For modifications outside a running simulation, use the following instead:

Editing parameters before a run: update_params() for a param.net object, or direct list assignment (e.g., p$inf.prob <- 0.5).
Editing init or control before a run: direct list assignment (e.g., ctrl$nsteps <- 1000), or rebuild with a fresh call to the init.net() / control.net() constructor.
Scheduled mid-simulation changes: the .param.updater.list argument to param.net() and the .control.updater.list argument to control.net(). See the "model-parameters" vignette for the underlying updater module and the scenario API built on top of it.

Mutability

The set_, append_, and add_ functions DO NOT modify the netsim_dat object in place. The result must be assigned back to dat in order to be registered: ⁠dat <- set_*(dat, item, value)⁠.

Examples

dat <- create_dat_object(control = list(nsteps = 150))
dat <- append_core_attr(dat, at = 1, n.new = 10)

dat <- add_attr(dat, "age")
dat <- set_attr(dat, "age", runif(10, 15, 65))
dat <- set_attr(dat, "status", rep(c("s", "i"), c(8, 2)))
get_attr_list(dat)
get_attr_list(dat, c("age", "active"))
get_attr(dat, "status")
get_attr(dat, "status", posit_ids = c(1, 9))

# Edit selected nodes
dat <- set_attr(dat, "status", "i", posit_ids = 3)
get_attr(dat, "status")

# Add 5 nodes: core attributes first, then the others
dat <- append_core_attr(dat, at = 2, n.new = 5)
dat <- append_attr(dat, "status", "s", 5)
dat <- append_attr(dat, "age", 15, 5)
get_attr(dat, "age")
get_attr(dat, "entrTime")

EpiModel documentation built on Oct. 16, 2026, 5:07 p.m.