Hello Team,   Am in the process of running a multivariate model with several continuous longitudinal responses. Am envisaging a wide format data structure with a number of responses, but currently working with two responses (S and D) as follows;   ID S1 S2 S3 S4 D1 D2 D3 D4 1 124 125 136 140 77 79 85 90 2 150 145 140 145 82 83 80 82 3 140 135 142 138 80 79 82 78   The 'S' and 'D' measurements are taken per individual at four time points (1, 2, 3, 4). The sample data set is from three individuals uniquely identified by 'ID'. Am able to restructure this to a long format  as follows; ID T S D 1 1 124 77 1 2 125 79 1 3 136 85 1 4 140 90 2 1 150 82 2 2 145 83 2 3 140 80 2 4 145 82 3 1 140 80 3 2 135 79 3 3 142 82 3 4 138 78   I now wish to combine the two sequences into one sequence (SDcomb) by a stack up procedure such that the resulting data set will appear as follows; ID T SDcomb 1 1 124 1 1 77 1 2 125 1 2 79 1 3 136 1 3 85 1 4 140 1 4 90 2 1 150 2 1 82 2 2 145 2 2 83 2 3 140 2 3 80 2 4 145 2 4 82 3 1 140 3 1 80 3 2 135 3 2 79 3 3 142 3 3 82 3 4 138 3 4 78   How do I achieve this? Thank you.   Kind Regards, MoZes ... View more