Select non-NA values from the Pandas dataframe.

Used to be like this.

iselect=np.nonzero(LMs.left_eye_center_x.notna() & LMs.right_eye_center_x.notna() &

         LMs.nose_tip_x.notna() & LMs.mouth_center_bottom_lip_x.notna())[0]

instead we can use dropna function.

iselect = LMs.dropna(subset=['left_eye_center_x', 'right_eye_center_x', 'nose_tip_x', 'mouth_center_bottom_lip_x'])

much simpler right?