Create a dagitty DAG using R-like syntax

dagify() creates dagitty DAGs using a more R-like syntax. It currently accepts formulas in the usual R style, e.g. y ~ x + z, which gets translated to y <- {x z}, as well as using a double tilde (~~) to graph bidirected variables, e.g. x1 ~~ x2 is translated to x1 <-> x2.

Usage

dagify(
  ...,
  exposure = NULL,
  outcome = NULL,
  latent = NULL,
  labels = NULL,
  coords = NULL
)

Arguments

...

formulas, which are converted to dagitty syntax

exposure

a character vector for the exposure (must be a variable name in the DAG)

outcome

a character vector for the outcome (must be a variable name in the DAG)

latent

a character vector for any latent variables (must be a variable name in the DAG)

labels

a named character vector, labels for variables in the DAG

coords

coordinates for the DAG nodes. Can be a named list or a data.frame with columns x, y, and name

Value

a dagitty DAG

Details

A single formula can mix the two: y ~ x + ~z gives x -> y and y <-> z. R's parser lets a unary ~ take in the rest of the right-hand side, so every term after the tilde is bidirected: y ~ x + ~z + w gives x -> y, y <-> z, and y <-> w, and y ~ ~x + z leaves both x and z bidirected. Parentheses limit how far the tilde reaches, so y ~ x + (~z) + w gives x -> y, y <-> z, and w -> y.

A term that is a call contributes one edge for each variable it mentions, so both y ~ f(x, z) and y ~ x:z give x -> y and z -> y.

See also

dag(), coords2df(), coords2list()

Examples

dagify(y ~ x + z, x ~ z)
#> dag {
#> x
#> y
#> z
#> x -> y
#> z -> x
#> z -> y
#> }

coords <- list(
  x = c(A = 1, B = 2, D = 3, C = 3, J = 3, E = 4, G = 5, H = 5, I = 5),
  y = c(A = 0, B = 0, D = 1, C = 0, J = -1, E = 0, G = 1, H = 0, I = -1)
)

dag <- dagify(
  G ~ ~H,
  G ~ ~I,
  I ~ ~G,
  H ~ ~I,
  D ~ B,
  C ~ B,
  I ~ C + J,
  J ~ B,
  B ~ A,
  H ~ E,
  C ~ E + G,
  G ~ D,
  coords = coords
)

dagitty::is.dagitty(dag)
#> [1] TRUE

ggdag(dag)


dag2 <- dagify(
  y ~ x + z2 + w2 + w1,
  x ~ z1 + w1,
  z1 ~ w1 + v,
  z2 ~ w2 + v,
  w1 ~ ~w2,
  exposure = "x",
  outcome = "y"
)

ggdag(dag2)