as_pcalg_constraints: Convert Knowledge to pcalg Knowledge

In causalDisco: Tools for Causal Discovery on Observational Data

Convert Knowledge to pcalg Knowledge

Description

pcalg only supports undirected (symmetric) background constraints:

• fixed_gaps - forbidding edges (zeros enforced)

• fixed_edges - requiring edges (ones enforced)

Usage

as_pcalg_constraints(kn, labels = kn$vars$var, directed_as_undirected = FALSE)

Arguments

kn	A Knowledge object. Must have no tier information.
labels	Character vector of all variable names, in the exact order of your data columns. Every variable referenced by an edge in kn must appear here.
directed_as_undirected	Logical (default FALSE). If FALSE, we require that every edge in kn has its mirror-image present as well, and will error if any are missing. If TRUE, we automatically mirror every directed edge into an undirected constraint.

Details

This function takes a Knowledge object (with only forbidden/required edges, no tiers) and returns the two logical matrices in the exact variable order you supply.

Value

A list with two elements, each an n × n logical matrix corresponding to pcalg fixed_gaps and fixed_edges arguments.

Errors

• If the Knowledge object contains tiered knowledge.

• If directed_as_undirected = FALSE and any edge lacks its symmetrical counterpart. This can only hold for forbidden edges.

See Also

Other knowledge functions: +.Knowledge(), add_exogenous(), add_tier(), add_to_tier(), add_vars(), as_bnlearn_knowledge(), 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

# pcalg supports undirected constraints; build a tierless knowledge and convert
data(tpc_example)

kn <- knowledge(
  tpc_example,
  child_x1 %!-->% youth_x3,
  youth_x3 %!-->% child_x1
)

pc_constraints <- as_pcalg_constraints(kn, directed_as_undirected = FALSE)
print(pc_constraints)

# error paths
# using tiers
kn <- knowledge(
  tpc_example,
  tier(
    child ~ starts_with("child"),
    youth ~ starts_with("youth"),
    oldage ~ starts_with("old")
  ),
  child_x1 %-->% youth_x3
)

try(as_pcalg_constraints(kn), silent = TRUE) # fails due to tiers

# using directed knowledge
kn <- knowledge(
  tpc_example,
  child_x1 %!-->% youth_x3
)

try(as_pcalg_constraints(kn), silent = TRUE) # fails due to directed knowledge

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