“…Single imputation refers to the use of a specific number (i.e., a best guess) in place of each missing value, which includes for example, k-nearest neighbor, mean/median imputation, smoothing, interpolation [21] and spline. Matrix completion and matrix factorization [5,6,7,24,20] are often used to impute panel data, as well as latent factor modelling [10,2,33]. Recently, there is a surge in the application of the recurrent neural network for imputation [9,11,22,8], as well as the generative adversarial network [34].…”