For my PhD, I am using PISA data from 2000, 2003 & 2018. My research focuses on SES achievement inequalities so I am therefore using the ESCS index. For 2000, the ESCS index is not included in the student file and has to be merged with the student file. However, I load both datasets in R, the ESCS file has more than double the observations. How do I merge these files?

but then my CSV changes and spaces are removed automatically and all letters get capitialized.Vos Viewer take this csv and get me with a wrong outputs. Also two column merge in a single column.

I am trying to merge a dataframe to an sf object, but having difficulties as the sf objects has a multipolygon vector column holding its co-ordinates and the dataframe has two different columns (x anf y) for its co-ordinates.