为什么需要嵌套if的范围（Len）？

Question

这是按原样工作的，但是当我没有range（len..）、do for i in arr和for j in arr时，我在if语句中得到IndexError: list index out of range。为什么会这样

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

不知道你试过什么。这应该以同样的方式工作：

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 2

当你迭代一个列表时，你会得到它的元素。因为您正在访问该元素索引处的列表元素，所以当它超出界限时，它将不起作用（而且无论如何也不会做您期望的事情）

相反，只需使用循环提供的项：

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 3

如果您以失败的形式分析代码的情况，您有：

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，该迭代器为您处理索引信息，因此您的“i”被设置为数组中的值

当你走到这条线时： if (arr[j] == arr[i]):

最后用变量替换arr[45]

数组的索引只会变为10，因此会抛出错误