how to select only those samples that meet two or more criteria
i want to create a new column using Day1_Orig values wherein there are both Day1_Orig and Day1_Repeat values for the same SUBJID. So for instance, lines 113 and 114 have same SUBJID, so the new column would record the value of the Day1_Orig value in line 113 (834), but as there is no corresponding Day1_Repeat value for line 107 (641), this Day1_Orig value would not be included in the new column.