add_exogenous: Add Exogenous Variables to Knowledge

In causalDisco: Tools for Causal Discovery on Observational Data

Add Exogenous Variables to Knowledge

Description

Adds variables that cannot have incoming edges (exogenous nodes). Every possible incoming edge to these nodes is automatically forbidden. This is equivalent to writing forbidden(everything() ~ vars).

Usage

add_exogenous(kn, vars)

add_exo(kn, vars)

Arguments

kn	A Knowledge object.
vars	Tidyselect specification or character vector of variables.

Value

Updated Knowledge object.

See Also

Other knowledge functions: +.Knowledge(), add_tier(), add_to_tier(), add_vars(), as_bnlearn_knowledge(), as_pcalg_constraints(), as_tetrad_knowledge(), convert_tiers_to_forbidden(), deparse_knowledge(), forbid_edge(), get_tiers(), knowledge(), knowledge_to_caugi(), remove_edge(), remove_tiers(), remove_vars(), reorder_tiers(), reposition_tier(), require_edge(), seq_tiers(), unfreeze()

Examples

data(tpc_example)

# create Knowledge object using verbs
kn1 <- knowledge() |>
  add_vars(names(tpc_example)) |>
  add_tier(child) |>
  add_tier(old, after = child) |>
  add_tier(youth, before = old) |>
  add_to_tier(child ~ starts_with("child")) |>
  add_to_tier(youth ~ starts_with("youth")) |>
  add_to_tier(old ~ starts_with("oldage")) |>
  require_edge(child_x1 ~ youth_x3) |>
  forbid_edge(child_x2 ~ youth_x4) |>
  add_exogenous(child_x1) # synonym: add_exo()

# set kn1 to frozen
# (meaning you cannot add variables to the Knowledge object anymore)
# this is to get a true on the identical check
kn1$frozen <- TRUE

# create identical Knowledge object using DSL
kn2 <- knowledge(
  tpc_example,
  tier(
    child ~ starts_with("child"),
    youth ~ starts_with("youth"),
    old ~ starts_with("oldage")
  ),
  child_x1 %-->% youth_x3,
  child_x2 %!-->% youth_x4,
  exo(child_x1) # synonym: exogenous()
)

print(identical(kn1, kn2))

# cannot require an edge against tier direction
try(
  kn1 |> require_edge(oldage_x6 ~ child_x1)
)

# cannot forbid and require same edge
try(
  kn1 |> forbid_edge(child_x1 ~ youth_x3)
)

causalDisco documentation built on April 13, 2026, 5:06 p.m.