Quantifying Nonlinear Dependence and Lead-Lag Dynamics via Chatterjee's Xi R package xiacf version 0.4.0 Computes Chatterjee's non-parametric correlation coefficient for time series data. It extends the original metric to time series analysis by providing the Xi-Autocorrelation Function (Xi-ACF) and Xi-Cross-Correlation Function (Xi-CCF). The package allows users to test for non-linear dependence using Iterative Amplitude Adjusted Fourier Transform (IAAFT) surrogate data. Main functions include xi_acf() and xi_ccf() for computation, along with matrix extraction tools. Methodologies are based on Chatterjee (2021) <doi:10.1080/01621459.2020.1758115> and surrogate data testing methods by Schreiber and Schmitz (1996) <doi:10.1103/PhysRevLett.77.635>. Software Imports: dplyr (>= 1.1.4), doFuture, foreach, future, ggplot2 (>= 4.0.1), latex2exp, progressr, Rcpp (>= 1.1.0), stats LinkingTo: Rcpp, RcppArmadillo Suggests: testthat (>= 3.3.2) Yasunori Watanabe <watanabe.yasunori@outlook.com> Comprehensive R Archive Network (CRAN) Yasunori Watanabe [aut, cre] MIT + file LICENSE (https://CRAN.R-project.org/package=xiacf/LICENSE) 2026-04-16 application/tgz https://CRAN.R-project.org/package=xiacf doi:10.32614/CRAN.package.xiacf