我正试图以角度拖放（ang-drag-drop）（[github angular-drag-drop] [1]）。如果接收器阵列为空，则示例不起作用。[plunkr] [2]。
example_vectorlist = [[1,2,4], [1,2,3], [3,4,3], [1,3,2], [5,6,7], [3,4,3], [5,6,7]]
# Desired output = [[1,2,4],[[1,2,3],[1,2,3]],[1,3,2],[[3,4,3], [3,4,3]],[[5,6,7], [5,6,7]]