A maximum marginal likelihood estimation with an expectation–maximization algorithm has been developed for estimating multigroup or mixture multidimensional item response theory models using the generalized partial credit function, graded response function, and 3‐parameter logistic function. The procedure includes the estimation of item parameters, attribute population distribution parameters, and test takers' attributes. All estimation functions and derivatives are provided. This procedure has been implemented in an R program. A simulation study has been conducted using this R program on various models related to the generalized partial credit function, and the result shows reasonable parameter recovery.