split into training set and test set with specific attribute values for rows

Question

My input file is under the following form:

gold,Attribute1,Attribute2
T,1,1
T,1,2
T,1,1
N,1,2
N,2,1
T,2,1
T,2,2
N,2,2
T,3,1
N,3,2
N,3,1
T,3,2
N,3,3
N,3,3
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