Fig. 2From: Machine learning methods to predict the cultivation age of Panacis Quinquefolii RadixSpatial distributions of the training set (red dots), test set 1 (green dots) and test set 2 (blue dots) after applying PCA. A Scatter plot in 3D space; B projection on three 2D planes. Feature space of test set 1 partially overlaps with that of the training set, whereas most samples in test set 2 fall outside the feature space of the training setBack to article page