Exploratory Trend Analysis and Visualization for Time-Series and Grouped Data R package trendtestR version 1.0.1 Provides a set of exploratory data analysis (EDA) tools for visualizing trends, diagnosing data types for beginner-friendly workflows, and automatically routing to suitable statistical tests or trend exploration models. Includes unified plotting functions for trend lines, grouped boxplots, and comparative scatterplots; automated statistical testing (e.g., t-test, Wilcoxon, ANOVA, Kruskal-Wallis, Tukey, Dunn) with optional effect size calculation; and model-based trend analysis using generalized additive models (GAM) for count data, generalized linear models (GLM) for continuous data, and zero-inflated models (ZIP/ZINB) for count data with potential zero-inflation. Also supports time-window continuity checks, cross-year handling in compare_monthly_cases(), and ARIMA-ready preparation with stationarity diagnostics, ensuring consistent parameter styles for reproducible research and user-friendly workflows.Methods are based on R Core Team (2024) <https://www.R-project.org/>, Wood, S.N.(2017, ISBN:978-1498728331), Hyndman RJ, Khandakar Y (2008) <doi:10.18637/jss.v027.i03>, Simon Jackman (2024) <https://github.com/atahk/pscl/>, Achim Zeileis, Christian Kleiber, Simon Jackman (2008) <doi:10.18637/jss.v027.i08>. Software Depends: R (>= 3.5.0) Imports: dplyr, ggplot2 (>= 3.3.0), lubridate, emmeans, e1071, forecast, MASS, multcomp, tidyselect, tidyr, tseries, car, FSA, ggpubr, rlang, splines, pscl, mgcv Suggests: testthat (>= 3.0.0), mockr, knitr, rmarkdown Gelan Huang <huanggelan97@icloud.com> Comprehensive R Archive Network (CRAN) Gelan Huang [aut, cre] GPL (>= 3) 2025-09-02 application/tgz https://CRAN.R-project.org/package=trendtestR doi:10.32614/CRAN.package.trendtestR