I have a table with two columns of number X and Y, and one column of strings called crystals.
crystals A A B C B D B C
Using ggplot2, how can I make a scatter plot of X versus Y with two types of points only, one shape for Crystals A, B, C and one shape for crystals D?
Tried to create subset but have not found a way to make 2 groups out of the 4 different values. I also tried to assign manually the same shape for A, B and C but then get a legend with the 4 entries instead of 2.