net-accessor: Functions to Access and Edit the Main netsim_dat Object in...

In EpiModel: Mathematical Modeling of Infectious Disease Dynamics

Functions to Access and Edit the Main netsim_dat Object in Network Models

Description

These get_, set_, append_, and add_ functions allow a safe and efficient way to retrieve and mutate the main netsim_dat class object of network models (typical variable name dat). They are intended for use inside module functions that run during a netsim() simulation, not for editing the user-facing param.net, init.net, or control.net inputs before a run or the output object returned by netsim(). See the Intended Usage section below for details and alternatives.

The accessors are documented on three pages, by the part of dat they act on:

• Nodal attributes, with one value per node (get_attr()): get_attr(), get_attr_list(), set_attr(), add_attr(), append_attr(), append_core_attr(), remove_node_attr(), and get_core_attributes().

• Epidemic outputs, with one value per time step (get_epi()): get_epi(), get_epi_list(), set_epi(), and add_epi().

• Parameters, control settings, and initial conditions (get_param()): get_param(), get_param_list(), set_param(), add_param(), the same four functions for control and init, and get_network_control().

Nodes are referred to by their positional identifiers; see get_unique_ids() and get_posit_ids() to convert them to and from their unique identifiers.

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)⁠.

set_ and append_ vs add_

The set_ and append_ functions edit a pre-existing element or create a new one if it does not exist already by calling the add_ functions internally.

See Also

update_params() for editing a param.net object outside a simulation; param.net(), init.net(), control.net() for input constructors; netsim() for running a simulation.

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