`emmeans` support fails for MMRMs fitted to data with only one (post baseline) visit

It is really great that the ANCOVA edge case (MMRM with only 1 post baseline visit) is supported by `mmrm` because it simplifies code significantly when I don’t have to condition on the number of post baseline visits. Ufortunately, it appears that `emmeans` support fails for this case. Please see the following example for details and let me know if you require additional information. Get packages: ``` r library(data.table) library(mmrm) library(emmeans) ``` Get data for first visit only: ``` r dt <- copy(fev_data) setDT(dt) mydata <- dt[AVISIT == "VIS1"] |> droplevels() mydata[, .N, AVISIT] #> AVISIT N #> <fctr> <int> #> 1: VIS1 200 ``` Fit ANCOVA model using `mmrm` (MMRM edge case): ``` r fm2 <- mmrm(FEV1 ~ FEV1_BL + ARMCD + us(AVISIT | USUBJID), data = mydata) ``` We can fit the model using `lm` to confirm that this is simply an ANCOVA: ``` r fm2_lm <- lm(FEV1 ~ FEV1_BL + ARMCD, data = mydata) all.equal(coef(fm2_lm), coef(fm2)) #> [1] TRUE all.equal(logLik(fm2), logLik(fm2_lm, REML=TRUE), check.attributes = FALSE) #> [1] TRUE ``` Unfortunately the `emmeans` support does not extend to the ANCOVA edge case: ``` r em <- try(emmeans(fm2, ~ ARMCD)) # Error related to factor levels #> Error in `contrasts<-`(`*tmp*`, value = contr.funs[1 + isOF[nn]]) : #> contrasts can be applied only to factors with 2 or more levels ``` This is what would have hoped for: ``` r emmeans(fm2_lm, ~ ARMCD) #> ARMCD emmean SE df lower.CL upper.CL #> PBO 32.4 0.794 131 30.8 33.9 #> TRT 36.9 0.806 131 35.3 38.5 #> #> Confidence level used: 0.95 ``` Session-info: ``` r sessionInfo() #> R version 4.5.2 (2025-10-31 ucrt) #> Platform: x86_64-w64-mingw32/x64 #> Running under: Windows 11 x64 (build 22631) #> #> Matrix products: default #> LAPACK version 3.12.1 #> #> locale: #> [1] LC_COLLATE=Danish_Denmark.utf8 LC_CTYPE=Danish_Denmark.utf8 #> [3] LC_MONETARY=Danish_Denmark.utf8 LC_NUMERIC=C #> [5] LC_TIME=Danish_Denmark.utf8 #> #> time zone: Europe/Copenhagen #> tzcode source: internal #> #> attached base packages: #> [1] stats graphics grDevices utils datasets methods base #> #> other attached packages: #> [1] emmeans_2.0.2 mmrm_0.3.17 data.table_1.18.2.1 #> #> loaded via a namespace (and not attached): #> [1] Matrix_1.7-4 compiler_4.5.2 Rcpp_1.1.1 splines_4.5.2 #> [5] yaml_2.3.12 fastmap_1.2.0 lattice_0.22-7 coda_0.19-4.1 #> [9] TH.data_1.1-5 generics_0.1.4 knitr_1.51 rbibutils_2.4 #> [13] MASS_7.3-65 backports_1.5.0 checkmate_2.3.3 rprojroot_2.1.1 #> [17] TMB_1.9.19 rlang_1.1.7 multcomp_1.4-29 xfun_0.55 #> [21] otel_0.2.0 estimability_1.5.1 cli_3.6.5 Rdpack_2.6.4 #> [25] digest_0.6.39 grid_4.5.2 rstudioapi_0.17.1 mvtnorm_1.3-3 #> [29] xtable_1.8-4 sandwich_3.1-1 nlme_3.1-168 evaluate_1.0.5 #> [33] codetools_0.2-20 zoo_1.8-15 survival_3.8-3 rmarkdown_2.30 #> [37] tools_4.5.2 htmltools_0.5.9 ```