+ struct string str;
+ int idx = i - cov->n_vars;
+ const struct interaction *iact =
+ categoricals_get_interaction_by_subscript (cov->categoricals, idx);
+ int df;
+
+ ds_init_empty (&str);
+ interaction_to_string (iact, &str);
+
+ df = categoricals_df (cov->categoricals, n);
+
+ tab_joint_text (t,
+ i, 0,
+ i + df - 1, 0,
+ TAT_TITLE, ds_cstr (&str));
+
+ if (i + df < tab_nr (t) - 1)
+ tab_vline (t, TAL_1, i + df, 0, tab_nr (t) - 1);
+
+ i += df;
+ n++;
+ ds_destroy (&str);