my_data = np.array([[0.5, 0.2, 0.1], ['NA', 0.45, 0.2], [0.9, 0.02, 'N/A']])
df = pd.DataFrame(my_data, dtype=str)
print(df.replace({'N': np.nan}, regex=True).astype(float))
Convert whole Pandas dataframe containing NaN values from string to float