semlbci (version 0.11.5)

syntax_to_i: Parameter Positions From lavaan Syntax

Description

Converts lavaan syntax to positions in the model parameter table.

Usage

syntax_to_i(syntax, sem_out)

Value

A numeric vector of positions (row numbers) in the parameter table.

Arguments

syntax

A vector of parameters, defined as in lavaan.

sem_out

The SEM output. Currently lavaan output only.

Details

syntax_to_i() converts a vector of strings, in lavaan syntax, to the positions in the parameter table of a lavaan::lavaan fit object.

Each element in the vector should have left hand side (lhs), operator (op), and/or right hand side (rhs). For example:all.x

• "m ~ x" denotes the coefficient of the path from x to m.

• "y ~~ x" denotes the covariance between y and x.

For user-defined parameters, only lhs and op will be interpreted. For example:

• To specify the user parameter ab, both "ab := ..." and "ab :=" will do, ... the definition of ab in the model. The right-hand side will be ignored.

To denote a labelled parameters, such as "y ~ a*x", treat it as a user-defined parameters and use :=, e.g., "a :=" in this example.

For multiple-group models, if a parameter is specified as in a single-group models, then this parameter in all groups will be selected. For example:all.x

• If a model has three groups, "y ~ x" denotes this path parameter in all three groups, and it will be converted to three row numbers.

To select the parameter in a specific group, "multiply" the right-hand-side variable by the group number. For example:

• "y ~ 2*x" denotes the path coefficient from x to y in Group 2.

To denote the parameters in more than one group, multiply the right-hand side variable by a vector of number. For example:all.x

• "f1 =~ c(2,3)*x2" denotes the factor loading of x2 on f1 in Group 2 and Group 3.

Elements that cannot be converted to a parameter in the parameter table will be ignored.

Currently supports lavaan::lavaan outputs only.

Examples

library(lavaan)
data(simple_med)
mod <-
"
m ~ a*x
y ~ b*m
ab:= a*b
asq:= a^2
"
fit_med <- sem(mod, simple_med, fixed.x = FALSE)
p_table <- parameterTable(fit_med)

pars <- c("m ~ x",
          "y ~ m",
          "asq := 1",
          "ab  := 2")
out <- syntax_to_i(pars, fit_med)
out
p_table[out, ]