| ptable_to_syntax {semhelpinghands} | R Documentation |
Convert a 'lavaan' Parameter Table to a 'lavaan' Model Syntax
Description
It tries to generate a
'lavaan' model syntax from a
lavaan parameter table.
Usage
ptable_to_syntax(object, allow_incomplete = FALSE)
compare_ptables(object1, object2)
Arguments
object |
If set to a |
allow_incomplete |
Whether
incomplete parameter table formed
by |
object1 |
The first |
object2 |
The second |
Details
This function tries to convert
a lavaan parameter table to a
text representation of the lavaan
model specified in model syntax.
When users call lavaan::sem(),
in addition to the model syntax,
other arguments not stored in the
syntax are also used to produce
the final model (e.g.,
meanstructure, fixed.x, and
std.lv). To produce exactly the
same model, these arguments are also
needed to be specified, which is
difficult to generate using only
the parameter table.
Therefore, the model syntax produced
will state all aspects of a model
explicitly, even for those aspects
that usually can be omitted due to
the default values of these arguments.
This approach requires users to call
lavaan::lavaan() directly, instead
of its wrappers (e.g, lavaan::sem()),
to produce the same parameter table.
The model syntax produced this way is more difficult to read. However, it ensures that original model can be reproduced, without the need to know the arguments to set.
Due to the nearly unlimited possibilities
in the form of a model, it is
recommended to compare the model
generated by the model syntax with
the original parameter table using
compare_ptables(). It
only compares the forms of the
two models, including user starting
values, if any. It does not compare
parameter estimates and standard
errors.
Raw Specification From lavaan::lavParseModelString()
There may be cases in which the
parameter table is the "incomplete"
table generated by lavaan::lavParseModelString(),
with as.data.frame. = TRUE.
This table is "incomplete" because
it is formed merely by parsing the
model syntax. There is no guarantee
that the model is valid.
The function ptable_to_syntax()
has basic support for this kind
of tables but it is disabled by
default. To process an incomplete
parameter table formed by
lavaan::lavParseModelString(),
set allow_incomplete to TRUE.
Limitations
The function ptable_to_syntax()
does not yet support the following
models:
Multiple-group models.
Multilevel models.
Models with categorical variables.
Models with user-specified lower or upper bounds.
Models with the operator
<~.Models with constraints imposed by
equal().Models with labels having spaces.
Models with labels having syntax operators (e.g.,
~,=~, etc.).
Value
ptable_to_syntax() returns a
length-one character vector that stores
the generated lavaan model syntax.
compare_ptables() returns a
length-one logical vector. TRUE
if the two models are identical
in form. FALSE if they are
not identical.
Functions
-
ptable_to_syntax(): Convert a lavaan parameter a lavaan model syntax. -
compare_ptables(): Compare two lavaan parameter tables.
Author(s)
Shu Fai Cheung https://orcid.org/0000-0002-9871-9448. This function is inspired by a discussion at the Google Group https://groups.google.com/g/lavaan/c/1ueFiue9qLM/m/cJhxDoqeBAAJ.
See Also
lavaan::lavaan(), lavaan::parameterTable()
Examples
library(lavaan)
mod <-
"
visual =~ x3 + x1 + x2
textual =~ x4 + x6 + x5
speed =~ x7 + x8 + x9 + start(0.1) * x6
visual ~ a*textual
speed ~ b*visual
ab := a * b
"
fit <- sem(mod, data = HolzingerSwineford1939)
mod_chk <- ptable_to_syntax(fit)
cat(mod_chk, sep = "\n")
# Need to call lavaan() directly
fit_chk <- lavaan(mod_chk, data = HolzingerSwineford1939)
fit_chk
fit
# Compare the parameter table:
(ptable1 <- parameterTable(fit))
(ptable2 <- parameterTable(fit_chk))
compare_ptables(ptable1, ptable2)