为什么我需要Range（Len））来嵌套if？

Question

这样可行，但当我没有范围（len ..））并且for i in arr和for j in arr时，我在if语句中得到IndexError: list index out of range。这是为什么？

arr = [2,2,2,2,4,5,2,45,3,4,4]

mostFrq = 0
mostFrqAmount = 0

for i in range(len(arr)):

        amountOfCurrent = 0

        # now look at temp element
        for j in range(len(arr)):
                if (arr[j] == arr[i]):
                        amountOfCurrent = amountOfCurrent + 1

        if (amountOfCurrent > mostFrqAmount):
                mostFrqAmount = amountOfCurrent
                mostFrq = arr[i]

print(mostFrq)
print(mostFrqAmount)

Answer 1

当您在列表上进行迭代时，您将获得其元素。既然您在该元素的索引处访问了列表元素，那么当它超出界限时它将无法工作（并且无法完成预期的操作）。

相反，只需使用循环提供的项目：

mostFrq = 0
mostFrqAmount = 0

for i in arr:
        amountOfCurrent = 0

        # now look at temp element
        for j in arr:
                if (j == i):
                        amountOfCurrent += 1

        if (amountOfCurrent > mostFrqAmount):
                mostFrqAmount = amountOfCurrent
                mostFrq = i

Answer 2

不确定您尝试了什么。这应该以相同的方式工作：

arr = [2,2,2,2,4,5,2,45,3,4,4]

mostFrq = 0
mostFrqAmount = 0

for i in arr:

        amountOfCurrent = 0

        # now look at temp element
        for j in arr:
                if (j == i):
                        amountOfCurrent = amountOfCurrent + 1

        if (amountOfCurrent > mostFrqAmount):
                mostFrqAmount = amountOfCurrent
                mostFrq = i

print(mostFrq)
print(mostFrqAmount)

Answer 3

如果您分析失败表单中代码的内容，您可以：

arr = [2,2,2,2,4,5,2,45,3,4,4]

mostFrq = 0
mostFrqAmount = 0

for i in arr:

        amountOfCurrent = 0

        # now look at temp element
        for j in arr:
                if (arr[j] == arr[i]):
                        amountOfCurrent = amountOfCurrent + 1

        if (amountOfCurrent > mostFrqAmount):
                mostFrqAmount = amountOfCurrent
                mostFrq = arr[i]

print(mostFrq)
print(mostFrqAmount)

使用for i in arr表单返回一个迭代器，为你处理索引信息，所以你的＆＃34; i＆＃34;设置为数组中的值。

当你到达这一行时：     if (arr[j] == arr[i]):

您最终使用arr[45]

的变量替换

您的数组索引只会变为10，因此，您会抛出错误。