使用for循环和if语句在未知索引情况下更改二维数组中的特定值。

huangapple
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英文:

Changing Specific Values In a 2D array Using For Loops and If statements without a known Index

问题

我有一个来自geotiff文件的2D数组。请参阅下面的示例数组：

  1. example_array = [[0, 1, 1, 0, 0, 0, 0],
  2.                  [2, 1, 1, 2, 0, 0, 0],
  3.                  [0, 3, 1, 1, 3, 0, 0],
  4.                  [4, 1, 1, 4, 0, 0, 0],
  5.                  [0, 5, 1, 1, 5, 0, 0],
  6.                  [0, 1, 1, 0, 0, 0, 0]]

我正在尝试编写一个程序，将每个嵌套列表中大于1的特定数字更改为'value + 100'。

在他人的帮助下，请查看下面的工作代码片段，它正确地将每个列表中第一个大于1的值更改为值+100。

  1. for l in example_array:
  2.     for i, x in enumerate(l):
  3.         if x > 1:
  4.             l[i] -= 100
  5.             break

如果我想要专门更改每个列表中大于1的第二个值，我尝试了下面的不正确代码片段：

  1. for l in example_array:
  2.     for i, x in enumerate(l):
  3.         if x > 1:
  4.             if x > 1:
  5.                 l[i] -= 100
  6.                 break

这里的思路是，如果我在for循环中添加另一个if x > 1:条件，它将从第一个大于1的数字开始，然后移动到下一个if x > 1:中大于1的第二个值。但在这里不是这种情况。有人有关于如何正确更改第二个大于1的数字的建议，以便显示下面的正确example_array吗？

  1. example_array = [[0, 1, 101, 0, 0, 0, 0],
  2.                  [2, 101, 1, 2, 0, 0, 0],
  3.                  [0, 3, 101, 1, 3, 0, 0],
  4.                  [4, 101, 1, 4, 0, 0, 0],
  5.                  [0, 5, 101, 1, 5, 0, 0],
  6.                  [0, 1, 101, 0, 0, 0, 0]]
英文:

I have a 2D array from a geotiff file. See the example array below:

  1. example_array = [[ 0, 1, 1, 0, 0, 0, 0], 
  2.                  [ 2, 1, 1, 2, 0, 0, 0], 
  3.                  [ 0, 3, 1, 1, 3, 0, 0], 
  4.                  [ 4, 1, 1, 4, 0, 0, 0], 
  5.                  [ 0, 5, 1, 1, 5, 0, 0], 
  6.                  [ 0, 1, 1, 0, 0, 0, 0]]

I am attempting to write a program that will change the specific number greater than 1 in each nested list to the 'value + 100'.

With the help of others see the below working code snippet that correctly changes the first value in each list greater than 1 to +100 of the value.

  1. for l in example_array:
  2.     for i, x in enumerate(l):
  3.         if x > 1:
  4.             l[i] -= 100
  5.             break

If I wanted to change exclusively the second value in each list greater than 1 I attempted the below incorrect code snippet:

  1. for l in example_array:
  2.     for i, x in enumerate(l):
  3.         if x > 1:
  4.             if x > 1:
  5.                 l[i] -= 100
  6.                 break

The thought process here is that if I added another if x>1: argument to the for loop it would start at the first number greater than 1 then move to the second value greater than 1 with the next if x>1:. That is not the case here. Does anyone have any suggestions on how to correctly change the second number greater that 1 such that is displays the correct example_array below?:

  1.     example_array = [[ 0,  1, 101, 0, 0, 0, 0], 
  2.                      [ 2, 101, 1,  2, 0, 0, 0], 
  3.                      [ 0,  3, 101, 1, 3, 0, 0], 
  4.                      [ 4, 101, 1,  4, 0, 0, 0], 
  5.                      [ 0,  5, 101, 1, 5, 0, 0], 
  6.                      [ 0,  1, 101, 0, 0, 0, 0]]

答案1

得分: 0

我假设在你的问题中，">=1" 的意思是大于等于1，而不是大于1，根据你提供的最后一个例子。这不是最优雅的解决方案，但我想这可能是你想要的：

  1. for l in example_array:
  2.     c = 0
  3.     for i, x in enumerate(l):
  4.         if x >= 1:
  5.             if c == 1:
  6.                 l[i] += 100
  7.                 break
  8.             c += 1

然而，你可以使用NumPy更高效地实现：

  1. import numpy as np
  3. # 假设example_array是一个列表的列表
  4. for row in example_array:
  5.     row_np = np.array(row)  # 将列表转换为NumPy数组以进行比较
  6.     positive_indices = np.where(row_np >= 1)[0]  # 获取大于等于1的元素的索引
  7.     if len(positive_indices) >= 2:  # 检查是否至少有两个大于等于1的元素
  8.         row[positive_indices[1]] += 100  # 在第二个大于等于1的元素上加100
英文:

I assumed for this response that you meant >=1 and not >1, judging by the final example you provided.

this is not the pretties solution but i guess it is what you're looking for:

  1. for l in example_array:
  2.     c = 0
  3.     for i, x in enumerate(l):
  4.         if x >= 1:
  5.             if c == 1:
  6.                 l[i] += 100
  7.                 break
  8.             c += 1

However you can do it much more efficiently using numpy:

  1. import numpy as np
  3. # Assuming example_array is a list of lists
  4. for row in example_array:
  5.     row_np = np.array(row)  # Convert list to NumPy array for the comparison
  6.     positive_indices = np.where(row_np >= 1)[0]  # Get indices of elements greater than or equal to 1
  7.     if len(positive_indices) >= 2:  # Check if there are at least two elements greater than or equal to 1
  8.         row[positive_indices[1]] += 100  # Add 100 to the second element greater than or equal to 1

huangapple
  • 本文由 发表于 2023年5月21日 05:57:10
  • 转载请务必保留本文链接：https://go.coder-hub.com/76297507.html
  • arrays
  • for-loop
  • if-statement
  • nested-lists
  • python
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