import numpy as npa = np.array([[1, 5, 6], [2, 4, 1], [3, 1, 5]])np.ma.MaskedArray(a, mask=(np.ones_like(a)*(a[:,0]==1)).T)# Returns: masked_array(data = [[-- -- --] [2 4 1] [3 1 5]], mask = [[ True True True] [False False False] [False False False]])



