README.md

In ctgimme: Continuous-Time Subgrouping with GIMME

ctgimme

ctgimme estimates group-, subgroup-, and individual-level continuous-time dynamic networks from intensive longitudinal data using continuous-time subgrouping GIMME (C-TSGIMME). It combines continuous-time state-space models with iterative searches for temporal paths supported across the sample, shared within recovered membership groups, or specific to individual subjects.

The method is described in:

Park, J. J., Fisher, Z. F., Hunter, M. D., Shenk, C., Russell, M., Molenaar, P. C. M., and Chow, S.-M. (2025). Unsupervised model construction in continuous-time. Structural Equation Modeling: A Multidisciplinary Journal, 32(3), 377--399. https://doi.org/10.1080/10705511.2024.2429544

Installation

Install the current release directly from GitHub:

if (!requireNamespace("remotes", quietly = TRUE)) {
  install.packages("remotes")
}
remotes::install_github("JPark93/ctgimme", dependencies = TRUE)

Install the 0.0.12 source archive while also resolving dependencies:

remotes::install_local(
  "path/to/ctgimme_0.0.12.tar.gz",
  dependencies = TRUE
)

If the dependencies are already installed, base R can install the archive:

install.packages(
  "path/to/ctgimme_0.0.12.tar.gz",
  repos = NULL,
  type = "source"
)

The imported dependencies, including OpenMx, are listed in DESCRIPTION. Package expm is required when subgroup.model = TRUE; igraph and nloptr support the optional legacy subgrouping workflow. Building or checking from a source checkout on Windows may require the Rtools version appropriate for the installed version of R.

Data requirements

The primary function, ctgimme(), expects a data frame in long format with one row per observation. The id and time arguments name the subject and observation-time columns, and varnames names the modeled variables. These columns may appear in any position. Identifier and time values must be nonmissing; observation times and nonmissing modeled values must be finite and numeric. Rows are not sorted internally, so they must already be ordered by time within subject. Missing modeled values are passed to OpenMx's raw-data likelihood.

The order of varnames determines the order of variables in the fitted drift and noise matrices. Subject identifiers are also used in intermediate filenames and therefore must be valid portable filename components. The identifier values must also remain unique when compared without case, because common Windows and macOS filesystems are case-insensitive. The selected time column is copied internally to a reserved column named Time; do not use Time as the name of a modeled process variable.

Basic use

library(ctgimme)

result <- ctgimme(
  varnames = c("x1", "x2", "x3"),
  dataframe = my_long_data,
  id = "subject_id",
  time = "observation_time",
  subgroup.method = "pam",
  sub.sig.thrsh = 0.55,
  max.subgroups = 4,
  cores = 1,
  directory = "ctgimme-output",
  verbose = TRUE
)

Set verbose = FALSE to suppress package progress messages and OpenMx optimizer reporting. Warnings and errors remain available through standard R condition handling, and the returned object and written artifacts are the same under either setting.

Search and subgroup controls

sig.thrsh = 0.55 requires a candidate group path to have significant modification-index support from at least 55% of subjects with usable results. Galpha = 0.05 supplies the base group-level significance threshold. The analogous subgroup defaults are sub.sig.thrsh = 1 and S.Galpha = 0.05, and the individual-level base threshold is Ialpha = 0.01. With the default ben.hoch = TRUE, these alpha values seed an adapted, progressively stricter threshold sequence for path additions; FALSE uses the corresponding alpha at every step. A group- or membership-group shared search adds no path when usable modification-index results are available for no more than half of the subjects requested for that search.

The default sub.sig.thrsh = 1 bypasses data-driven subgroup detection and assigns all subjects to membership group 1. It does not skip the subsequent within-group shared-path search or individual-model fits. Set it below one to activate subgroup.method. The default method, "pam", screens recurrent signed evidence for eligible non-group paths, computes mean Manhattan distances, and selects the candidate with the largest average silhouette width. Active PAM subgrouping requires max.subgroups to be an integer of at least two; the actual upper candidate count is also limited to one less than the number of subjects with usable features. Its recurrence screen uses fixed 0.05 subject-evidence and BH-adjusted recurrence thresholds, independently of ben.hoch.

The alternative subgroup.method = "legacy" uses a weighted similarity graph and Walktrap community detection and requires igraph. With conduct = TRUE, the default, its graph cutoff is optimized with nloptr; set conduct = FALSE to use the unoptimized similarity weights shifted to start at zero.

Set scale.data = TRUE to standardize each modeled variable separately within subject before all estimation stages. The default is FALSE; constant within-subject columns are centered to zero when scaling is requested.

Noise variances

By default, measurement-error and process-noise variances are fixed at the values supplied through ME.var and PE.var: ME.var defaults to 1e-8, whereas PE.var = NULL produces an identity matrix. Set ME.free = TRUE or PE.free = TRUE to estimate every diagonal variance, using the corresponding variance argument as its starting value. Logical vectors allow selective estimation in the order given by varnames:

result <- ctgimme(
  varnames = c("x1", "x2", "x3"),
  dataframe = my_long_data,
  id = "subject_id",
  time = "observation_time",
  directory = "ctgimme-output",
  ME.var = 0.05,
  ME.free = FALSE,
  PE.var = 1,
  PE.free = c(TRUE, TRUE, FALSE)
)

Only diagonal measurement-error and process-noise variances are supported; off-diagonal covariances remain fixed to zero. Estimating both sets of variances can require substantially more within-person information than estimating process noise while fixing measurement error. Estimated process-noise and measurement-error variances are stored in the Q and R matrices, respectively, of each saved OpenMx model.

Optional joint membership-group models

The default subgroup.model = FALSE skips only the additional joint, parameterized model for each membership group; subgroup-level structural searches and individual fits still run. Set it to TRUE to fit one shared-parameter model per subgroup and write its coefficient plot, discrete-time transition plots, and fitted-model RDS file. This workflow requires expm.

result <- ctgimme(
  ...,
  subgroup.model = TRUE,
  time.intervals = c(0.25, 1, 2)
)

The subgroup model is estimated from the summed likelihoods of its members. Each member has an independently initialized continuous-time state-space filter, so no state is propagated across subject boundaries and no trajectories are concatenated. The saved result is one fitted OpenMx model with one top-level A, Q, and R; its subject children are likelihood blocks, not separately estimated parameter models. This creates one fitted joint model for each subgroup, not one fitted parameter model per member. Each subject's observation times are rebased to its first observation, preserving all within-person elapsed intervals while removing arbitrary calendar offsets.

time.intervals remains the only subgroup-model time control. For every requested nonnegative delta t, ctgimme computes exp(A * delta_t) and writes the discrete-time transition plot. For subgroup g, the files are written to Models/Subgroup <g>/ with these names:

• Subgroup <g> Params.png;
• Subgroup <g> Delta_t = <delta>.png for every requested delta t; and
• Subgroup_<g>Model.RDS, containing the single fitted joint model.

OpenMx and RStudio compatibility

All internal mxTryHard() calls pass through one package wrapper. With verbose = TRUE, package stage messages and ordinary optimizer reporting from fits in the main R process are shown; PSOCK workers do not forward raw console output. With verbose = FALSE, package messages and main-process OpenMx output are suppressed so a quiet run remains quiet. Subgroup parameter plots also supply edge labels as a square matrix, as required by qgraph for the fitted drift matrix. Parameter and transition plots use expanded margins so boundary nodes, loops, titles, and labels are not clipped in the saved PNG files.

For a first run on a new computer, use cores = 1 and a new, empty output directory. After that run succeeds, cores = 2 can reduce elapsed time, at the cost of the memory used by one additional R/OpenMx worker. Requests above two are reduced to the package-wide two-worker maximum.

Results and output files

When enabled subgroup detection succeeds, the function returns the selected PAM or Walktrap clustering object. Both forms carry the complete, ID-aligned vector in attr(result, "ctgimme.membership"); PAM results additionally expose the same vector as result$membership. If PAM has fewer than three usable subject model/MI pairs or no recurrent eligible features, or legacy detection has fewer than two usable pairs, detection falls back to one membership group and the function invisibly returns a result list containing the complete membership, group structure, output directory, and subgroup diagnostics. A successfully computed legacy solution may itself contain one community and still returns its communities object.

When sub.sig.thrsh = 1, the same result-list form includes the group structure, complete membership vector, output directory, subgroup-detection record, and completion message. Thus every successful return directly exposes the complete membership. Every successfully completed run also saves it to subgroup_membership.csv and subgroup_detection.rds. Subjects without usable model/MI artifacts are assigned to group 1 in these complete outputs.

The output directory includes:

• GStruc.RDS, containing the group-level structure;
• SGStruc*.RDS, containing the shared structure for each membership group, including the single group used when detection is disabled or falls back;
• subgroup_membership.csv, mapping every subject identifier to a subgroup;
• Subgroups Plot.png, showing a subject-distance map when diagnostic distances are available and a complete membership roster otherwise;
• subgroup_detection.rds, containing subgroup diagnostics; and
• successfully fitted final subject models and plots in Models/Individuals.

Successful PAM detection also writes pam_silhouette_selection.png; successful legacy detection writes walktrap_community_plot.png. With subgroup.model = TRUE, each successfully fitted membership-group model is written as Subgroup_<g>Model.RDS, together with Subgroup <g> Params.png and one Subgroup <g> Delta_t = <delta>.png for every requested delta t. By default, keep.intermediate = FALSE removes temporary per-subject Model_<id>.RDS and MI_<id>.RDS search files after successful completion; final individual and pooled membership-group models are retained.

For PAM subgrouping, the plot uses classical multidimensional scaling of the same mean Manhattan distances used for clustering. Mapped subjects that are closer in the plot have more similar recurrent-evidence profiles. Colors and enclosing hulls show subgroup membership, while nearest-neighbor edges aid visual interpretation. The two-dimensional display is an approximation; its reported goodness-of-fit summarizes how well it represents the full distance matrix. Subjects lacking a diagnostic distance are named on the plot but are not placed on the map.

Parallel execution

The cores argument defaults to one. Explicit requests are bounded by both the number of subjects and a package-wide maximum of two workers, in accordance with CRAN policy. OpenMx is set to one thread in each R process during the run, and the calling process's previous OpenMx thread setting is restored on exit.

For cores > 1, ctgimme creates one PSOCK worker pool and reuses it for the group, subgroup, and individual fitting batches. Workers load OpenMx and qgraph once, wait idle while the main R process pools modification indices and selects the next path or subgroup, and then receive the next fitting batch. The pool is stopped when the analysis finishes or exits with an error.

Quick demonstration

ctgimme_demo() provides a deterministic, lightweight demonstration of the feature-selection and subgrouping logic without fitting OpenMx models:

demo <- ctgimme_demo()
demo$membership
demo$candidates

The demonstration avoids OpenMx fitting and deterministically recovers its known two-subgroup partition.

Citation

Use the package citation and its methodological reference with:

citation("ctgimme")

Development

See the contributing guide for the test and pull-request workflow. Release notes are maintained in NEWS.md.

Authors and license

ctgimme is authored by Jonathan J. Park ([e-mail]) and Nathan Xin Mills ([e-mail]). The package is distributed under the Apache License 2.0.

ctgimme documentation built on Aug. 24, 2026, 5:13 p.m.