[英]How can I get value from 2d array? - Python
I had a 2D array where every row has 2 elements: 我有一个2D数组,其中每一行都有2个元素:
R3 = [
[[0, 4, 4, ...]
[[0, 0, 0, ...]
[[4, 0, 0, ...]
]
And this is the position of elements of the 2D array. 这是2D数组元素的位置。
whereR3 = [
[0, 1],
[0, 2],
[1, 4],
[1, 34],
[2, 0],
[2, 5],
[3, 8],
[3, 9],
[4, 12],
]
I want to do subtract the second element of a row from the first element, but the bottleneck is getting the value in a certain position from the 2D array. 我想从第一个元素中减去行的第二个元素,但瓶颈是从2D数组中的某个位置获取值。 Here's what I've tried:
这是我尝试过的:
print(R3[0][1] - R3[0][2])
With this code, I can't calculate through every row and can't do it in a loop. 使用此代码,我无法遍历每一行,也无法循环执行。
You can easily used nested for loops like this: 您可以像这样轻松地使用嵌套的for循环:
for list_ in R3:
for number in list_:
print(number - list_[1]) #if you know that every row has array of 2 elements
Python indexes from 0, so you'll need to select positions 0 and 1 instead of 1 and 2. You can do that pretty easily in a for
loop like this: Python从0开始索引,因此您需要选择位置0和1而不是1和2。您可以在
for
循环中轻松地做到这一点,如下所示:
for row in whereR3:
print(row[0] - row[1])
If you want a new list where each row has been collapsed to row[0] - row[1]
, you can use a list comprehension: 如果您想要一个新的列表,其中的每一行都已折叠为
row[0] - row[1]
,则可以使用列表推导:
collapsed_R3 = [row[0] - row[1] for row in whereR3]
When executed, collapsed_R3
will be equal to: 执行后,
collapsed_R3
将等于:
[-1, -2, -3, -33, 2, -3, -5, -6, -8]
And to get a specific row's collapsed value (row 0, for example): 并获取特定行的折叠值(例如,行0):
whereR3[0][0] - whereR3[0][1]
Which is equal to -1
. 等于
-1
。 The first slice ( [0]
on both sides) selects the row, and the second slice ( [0]
and [1]
) are selecting the item within the row. 第一个切片(两侧均为
[0]
)选择该行,第二个切片( [0]
和[1]
)选择该行中的项目。
result = [y- x for x,y in R3]
[1, 2, 3, 33, -2, 3, 5, 6, 8]
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