我有一个数据帧，部分是这样复制的：import pandas as pd

import numpy as np

tab = pd.DataFrame(np.array([[ 46, 39, 25, 29, 21, 12, 33, 32, 70, 109, 144, 158, 161,

184, 163, 113, 117, 82, 76, 88, 77, 76, 64, 35],

[ 39, 33, 29, 29, 26, 14, 25, 33, 60, 83, 126, 117, 111,

148, 141, 104, 92, 75, 78, 74, 63, 67, 52, 39],

[ 30, 27, 14, 11, 20, 17, 21, 31, 48, 62, 83, 78, 88,

90, 80, 67, 53, 61, 47, 54, 50, 48, 35, 26],

[ 30, 24, 19, 15, 17, 10, 12, 18, 34, 69, 88, 79, 109,

95, 89, 82, 53, 46, 53, 57, 39, 41, 26, 29],

[ 37, 31, 18, 12, 30, 13, 15, 19, 51, 61, 74, 81, 77,

100, 96, 74, 60, 57, 42, 48, 43, 40, 29, 25],

[ 14, 8, 14, 11, 13, 7, 9, 15, 42, 49, 50, 44, 53,

42, 31, 31, 30, 27, 33, 25, 27, 17, 20, 17],

[ 10, 15, 6, 10, 15, 11, 7, 18, 28, 43, 49, 37, 41,

33, 37, 32, 26, 28, 19, 24, 19, 19, 13, 18],

[ 9, 9, 8, 12, 7, 11, 4, 8, 14, 15, 23, 30, 29,

34, 25, 39, 22, 20, 15, 23, 12, 19, 14, 13],

[ 0, 3, 4, 1, 1, 0, 3, 4, 4, 5, 3, 5, 6,

7, 3, 3, 6, 4, 2, 3, 3, 2, 2, 2],

[ 3, 0, 1, 0, 0, 0, 1, 1, 4, 8, 2, 4, 7,

2, 2, 9, 3, 5, 1, 5, 2, 0, 4, 1]]), index =

['Stadsdeel Zuid', 'Stadsdeel West', 'Stadsdeel Nieuw-West',

'Stadsdeel Centrum', 'Stadsdeel Oost', 'Stadsdeel Noord',

'Wijk 00 Amstelveen', 'Stadsdeel Zuidoost', 'Wijk 00',

'Wijk 00 Aalsmeer'])

我画了一张热图

^{pr2}$

我希望锚定colormap的值是基于每行的min-max-values的值，这样具有较低值的行也是可见的。(实际上，该表包含更多的低值行，热图几乎没有显示颜色)

如何做到这一点？在