Bug with summary.MxModel in saved workspace

I've encountered the same behavior. The solution you mentioned is the only one I've come up with: just write require(OpenMx) before looking at OpenMx objects. It seems like the R workspace is not saving the fact that OpenMx was loaded. Running a single line of code is not an onerous task for the fix, but I'm curious to hear if other developers and R experts have a better solution.

I am running the below version of OpenMx in R version 3.3.1, and I still get the uninformative summary
Length Class Mode
1 MxRAMModel S4

even when I try the fixes above (opening R first, require(OpenMx), etc.) this does not fix the problem. The models appear to be running, but I can't get the summary

OpenMx version: 2.7.4 [GIT v2.7.4]
R version: R version 3.3.1 (2016-06-21)
Platform: x86_64-w64-mingw32
Default optimiser: CSOLNP

> R.Version()
$platform
[1] "x86_64-w64-mingw32"

$arch
[1] "x86_64"

$os
[1] "mingw32"

$system
[1] "x86_64, mingw32"

$status
[1] ""

$major
[1] "3"

$minor
[1] "3.1"

$year
[1] "2016"

$month
[1] "06"

$day
[1] "21"

$`svn rev`
[1] "70800"

$language
[1] "R"

$version.string
[1] "R version 3.3.1 (2016-06-21)"

$nickname
[1] "Bug in Your Hair"

Thanks for any help, as I am teaching from the Grimm, Ram & Estabrook text and we will be using OpenMx soon!!!

I can confirm most of the behavior jcromley reports, but for me
quit R (if it's running)
start R
library(OpenMx)
load .RData file
summary(AnOpenMxModel)

works fine. Attempting to summary the model before OpenMx is loaded, or loading OpenMx after the .RData file has been loaded fails with the uninformative summary about what the object is. That seems like a bug to me: OpenMx version: 2.7.4.5 [GIT v2.7.4-5-g0e2ecaf].

Note again that a change of OpenMx version between saving the .RData and loading it again can cause issues. OpenMx lacks backward compatibility with mxModel objects (especially ones that have been mxRun()) which is a pity. Typically the error in this case is even more cryptic, but different from the length/class/mode info one you have been getting.

This specifically appears to be an issue with S4 object classes that extend the MxModel class. I believe only two exist in OpenMx, MxRAMModel and MxLISRELModel, of which MxRAMModel is by far the more frequently used. Compare the two attached scripts. If you run loadtest--181129b.R , quit R (after clearing its workspace if using RStudio), restart R, load the saved workspace, and run `summary(factorModelFit)`, the `summary()` generic correctly uses the method defined for class MxModel (because OpenMx was automatically loaded with the saved workspace). On the other hand, if you run loadtest--181129.R , quit R (after clearing its workspace if using RStudio), restart R, load the saved workspace, and run `summary(factorModelFit)`, `summary()` does not work the way it is supposed to.

Also notice that in both scripts, `fm1`, which is an instance of class merMod from lme4, works correctly with `summary()`. Class merMod differs from MxRAMModel in at least two respects. For one thing, merMod extends object classes from the stats package, and R's out-of-the-box default calls for stats to be loaded into R's workspace when R starts up. Second, merMod is an S3 class, not an S4 class.

FWIW:

> mxVersion()
OpenMx version: 2.11.5.78 [GIT v2.11.5-78-ge4567187-dirty]
R version: R version 3.4.4 (2018-03-15)
Platform: x86_64-pc-linux-gnu
Default optimizer: CSOLNP
NPSOL-enabled?: Yes
OpenMP-enabled?: Yes


I do understand how obnoxious to some users it must be to have to remember to load the OpenMx package before restoring their saved workspace. So, I tried again today to make it possible for `summary()` to work properly with an MxRAMModel object that's been loaded into R's workspace before OpenMx is. I consulted the 'Methods_for_s3' entry in the documentation for the 'methods' package, and followed as best I could its advice for dispatching S3 methods with S4 classes. All to no avail.

I think this issue must have something to do with how OpenMx constructs objects of class "MxRAMModel". I think it's significant that if you run `str()` on an MxRAMModel object, no associated package is reported.

Good news: I think I've FINALLY figured out the cause of this bug!

It's looking pretty likely that this bug will be repaired in the next stable release of OpenMx. Until then, there's a workaround! For example, try running loadtest--181129.R, and let it save the workspace to disk. Then, restart R, and load the saved workspace. After that, run the following 3 lines:

foo <- "MxRAMModel"
attr(foo,"package") <- "OpenMx"
class(factorModelFit) <- foo

`summary()`will then work correctly on `factorModelFit`.

This bug is repaired in the v2.13.2 release, which was just announced today.