Hi,   I was given 2 data files containing variables of similar participants (slightly different due to participants dropping out over time). However, the same participants have different ID in each file, eg. ID 1784636 in one file is ID 1000015 in the other file, but they represent the same participant. There are over 500,000 participants in my file so can't match them individually. I do have an Excel file showing which ID in file 1 matches with which ID in file 2. Therefore, I was wondering is there any code that I could use to merge my 2 files using this information? Thank you!   Best wishes Gewei ... View more