如何将嵌套列表中的浮点数舍入到小数点后两位？

Question

我有几个多边形的坐标列表，如下所示：

l_b =  [[[57.5, 2.875],
   [83.75, 4.1875],
   [83.75, 18.70923913043478],
   [57.50000000000001, 18.70923913043478],
   [57.5, 2.875]],
  [[83.75, 18.70923913043478],
   [57.50000000000001, 18.70923913043478],
   [57.5, 34.08695652173913],
   [83.75, 34.54347826086956],
   [83.75, 18.70923913043478]],
  [[0.0, 0.0],
   [18.125, 0.90625],
   [18.125, 16.70108695652174],
   [-2.530467720685112, 16.70108695652174],
   [0.0, 0.0]],
  [[18.125, 16.70108695652174],
   [-2.530467720685112, 16.70108695652174],
   [-5.0, 33.0],
   [18.125, 33.40217391304348],
   [18.125, 16.70108695652174]]]

如何在保持格式不变的情况下将列表中的所有数字四舍五入到小数点后两位？

我试过 l_b = [ '%.2f' % elem for elem in l_b ] 但它给了我 TypeError: must be real number, not list

Answer 1

您有 3 层嵌套列表，因此您需要向下钻取

l_b = [[['%.2f' % y[0], '%.2f' % y[1]] for y in x] for x in l_b]

Answer 2

@Guy 的解决方案有一个副作用。它使列表变平。

这个可能更合适。

l_b = [[['%.2f' % z for z in y] for y in x] for x in l_b]

Answer 3

如果您的列表是任意嵌套的，您可以使用递归。如果您的列表是 3 级嵌套，则使用@Guy 的答案或@mrEvgenX 的答案。

In [51]: def recur(lst):
    ...:     if isinstance(lst,float):
    ...:         return '%.2f'%lst #use round(lst,2) if you want float instead of string.
    ...:     else:
    ...:         return [recur(i) for i in lst]

In [52]: recur(l_b)

输出

[[['57.50', '2.88'],
  ['83.75', '4.19'],
  ['83.75', '18.71'],
  ['57.50', '18.71'],
  ['57.50', '2.88']],
 [['83.75', '18.71'],
  ['57.50', '18.71'],
  ['57.50', '34.09'],
  ['83.75', '34.54'],
  ['83.75', '18.71']],
 [['0.00', '0.00'],
  ['18.12', '0.91'],
  ['18.12', '16.70'],
  ['-2.53', '16.70'],
  ['0.00', '0.00']],
 [['18.12', '16.70'],
  ['-2.53', '16.70'],
  ['-5.00', '33.00'],
  ['18.12', '33.40'],
  ['18.12', '16.70']]]

Answer 4

您可以使用 round 带有列表理解的内置函数：

l_b = [[[round(e, 2) for e in j] for j in i] for i in l_b]

Answer 5

试试这个 numpy 方法：

l_b = np.array( [[[57.5, 2.875],
   [83.75, 4.1875],
   [83.75, 18.70923913043478],
   [57.50000000000001, 18.70923913043478],
   [57.5, 2.875]],
  [[83.75, 18.70923913043478],
   [57.50000000000001, 18.70923913043478],
   [57.5, 34.08695652173913],
   [83.75, 34.54347826086956],
   [83.75, 18.70923913043478]],
  [[0.0, 0.0],
   [18.125, 0.90625],
   [18.125, 16.70108695652174],
   [-2.530467720685112, 16.70108695652174],
   [0.0, 0.0]],
  [[18.125, 16.70108695652174],
   [-2.530467720685112, 16.70108695652174],
   [-5.0, 33.0],
   [18.125, 33.40217391304348],
   [18.125, 16.70108695652174]]])

数组的形状是(4,5,2)

应用地图将小数点四舍五入到 2 位

a=list(map(lambda x :round(x,2),l_b.flatten() ))

变回原来的形状

np.array(a).reshape(4,5,2)

或

Georgy

建议的更简单的方法

l_b.round(2)

Answer 6

您可以将 map() 与 round() 一起使用。 round() 可以将所需的位数作为第二个参数。

for polygon in l_b:
    for point in polygon:
        point[:] = map(lambda x: round(x, 2), point)

如何将嵌套列表中的浮点数舍入到小数点后两位？

How to round floats in a nested list to 2 decimal places?

python

rounding

nested-lists

coordinates