Running the Mlogit function does not work, because it says that the two indexes(Resp_id & Alternative_id) are not unique. I have twelve times the same ID, because each respondent got 12 choice options with 3 alternatives.

> cbc_mlogit <- mlogit.data(thesis, 
+                           choice = "Selection",  # Choice variable
+                           shape = "long",       # Convert to long format
+                           alt.var = "Alternative_id",  # Alternative ID variable
+                           id.var = "Resp_id")       # Respondent ID variable
Error: Error in dfidx::dfidx(data = data, dfa$idx, drop.index = dfa$drop.index,  : 
  the two indexes don't define unique observations

Dataset looks like this

Desired output: get partworth utilities

I tried to make Resp_id and Alternative_id a character (now numeric), but still the same issue