在 Python 3 中迭代数组
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Iterating over arrays in Python 3
提问by q-compute
I haven't been coding for awhile and trying to get back into Python. I'm trying to write a simple program that sums an array by adding each array element value to a sum. This is what I have:
我有一段时间没有编码并试图重新使用 Python。我正在尝试编写一个简单的程序，通过将每个数组元素值添加到总和来对数组求和。这就是我所拥有的：
def sumAnArray(ar):
theSum = 0
for i in ar:
theSum = theSum + ar[i]
print(theSum)
return theSum
I get the following error:
我收到以下错误：
line 13, theSum = theSum + ar[i]
IndexError: list index out of range
I found that what I'm trying to do is apparently as simple as this:
我发现我想要做的事情显然就像这样简单：
sum(ar)
But clearly I'm not iterating through the array properly anyway, and I figure it's something I will need to learn properly for other purposes. Thanks!
但很明显，无论如何我都没有正确地遍历数组，我认为这是我需要为其他目的正确学习的东西。谢谢！
回答by Mr Alihoseiny
When you loop in an array like you did, your for variable(in this example i) is current element of your array.
当你像你一样在数组中循环时，你的 for 变量（在这个例子中i）是数组的当前元素。
For example if your aris [1,5,10], the ivalue in each iteration is 1, 5, and 10.
And because your array length is 3, the maximum index you can use is 2. so when i = 5you get IndexError.
You should change your code into something like this:
例如，如果你的ar就是[1,5,10]，将i在每次迭代中值是1，5和10。因为你的数组长度是 3，所以你可以使用的最大索引是 2。所以当i = 5你得到IndexError. 你应该把你的代码改成这样：
for i in ar:
theSum = theSum + i
Or if you want to use indexes, you should create a range from 0 ro array length - 1.
或者，如果您想使用索引，您应该从 0 ro 创建一个范围array length - 1。
for i in range(len(ar)):
theSum = theSum + ar[i]
回答by umluizlima
The for loop iterates over the elements of the array, not its indexes. Suppose you have a list ar = [2, 4, 6]:
for 循环遍历数组的元素，而不是它的索引。假设您有一个列表 ar = [2, 4, 6]：
When you iterate over it with for i in ar:the values of i will be 2, 4 and 6. So, when you try to access ar[i]for the first value, it might work (as the last position of the list is 2, a[2] equals 6), but not for the latter values, as a[4] does not exist.
当您使用for i in ar:i 的值对其进行迭代时， i 将是 2、4 和 6。因此，当您尝试访问ar[i]第一个值时，它可能会起作用（因为列表的最后一个位置是 2，a[2] 等于 6 )，但不适用于后面的值，因为 a[4] 不存在。
If you intend to use indexes anyhow, try using for index, value in enumerate(ar):, then theSum = theSum + ar[index]should work just fine.
如果您打算无论如何使用索引，请尝试使用for index, value in enumerate(ar):，然后theSum = theSum + ar[index]应该可以正常工作。
回答by ajay mathur
You can use
您可以使用
nditer
Here I calculated no. of positive and negative coefficients in a logistic regression:
在这里我计算了没有。逻辑回归中的正负系数：
b=sentiment_model.coef_
pos_coef=0
neg_coef=0
for i in np.nditer(b):
if i>0:
pos_coef=pos_coef+1
else:
neg_coef=neg_coef+1
print("no. of positive coefficients is : {}".format(pos_coef))
print("no. of negative coefficients is : {}".format(neg_coef))
Output:
输出：
no. of positive coefficients is : 85035
no. of negative coefficients is : 36199
回答by Faizi
While iterating over a list or array with this method:
使用此方法迭代列表或数组时：
ar = [10, 11, 12]
for i in ar:
theSum = theSum + ar[i]
You are actually getting the values of list or array sequentially in ivariable.
If you print the variable iinside the for loop. You will get following output:
您实际上是在i变量中按顺序获取列表或数组的值。如果i在for loop. 您将获得以下输出：
10
11
12
However, in your code you are confusing ivariable with index value of array. Therefore, while doing ar[i]will mean ar[10]for the first iteration. Which is of course index out of range throwing IndexError
但是，在您的代码中，您将i变量与数组的索引值混淆了。因此，while doar[i]将意味着ar[10]进行第一次迭代。这当然是索引超出范围抛出IndexError
EditYou can read thisfor better understanding of different methods of iterating over array or list in Python
编辑您可以阅读本文以更好地理解在 Python 中迭代数组或列表的不同方法
