Question

我想如何从列表列表中找到偶数例子是：

maximum_even_each_list_in_lol([[1,2,3],[6,5,4],[5,7,9]])

应返回（最大偶数）：

[2,6,0]

我找到了如何从stackoverflow中找到列表中的偶数：

def maximum_even_each_list_in_lol (lol):
    evens=[]
    for number in lol:
        if is_even(number):
            evens.append(number)
    return evens

但我想知道如何制作它以便它可以在列表中找到每个列表中的偶数。

Answer 1

虽然您没有明确说出来，但似乎您正在查找列表列表中每个列表中的最大偶数。从你的例子来看，如果没有偶数，你似乎希望程序加0。在这种情况下，这将起作用：

print [max(value for value in [0] + L if not value % 2) for L in list_of_lists]

Answer 2

您可以使用一些不错的Pythonic语言结构从内到外构建此算法：

# Function to determine if one number is even
is_even = lambda x : x%2==0

# Function to return just the even numbers of a list
just_evens = lambda x : filter(is_even, x)

# Function to return the maximum number in a list, or '0' if there is none
get_max = lambda x : max(x) if len(x) else 0

# Function to return the maximum even number of a list
max_even = lambda x : get_max(just_evens(x))

# Print out the maximum even number from each list:
map(max_even, [[1,2,3],[6,5,4],[5,7,9]])

这将打印出来：

[2, 6, None]

Answer 3

python 3.4采用max的默认值，因此如果在过滤后没有偶数，我们可以将0作为默认值返回：

l = [[1,2,3],[6,5,4],[5,7,9]]
print([max(filter(lambda x: not x % 2,x),default=0) for x in l])
[2, 6, 0]

Answer 4

你快到了！的： - ）

检查内置max函数的功能。

def maximum_even_each_list_in_lol (lol): evens=[0] # Dirty trick to ensure that regardless of the `even` numbers # found, you'll always have a zero among the results. for number in lol: if is_even(number): evens.append(number) print "I found these even numbers (%s) among %s" % (evens, lol) return max(evens) # Return the maximum value among the `evens` list. results = [] for lst in [[1,2,3],[6,5,4],[5,7,9]]: print "Studying %s" % lst results.append(maximum_even_each_list_in_lol(lst)) print "This is what I found: %s" % results

我添加了一些print语句来帮助您了解代码的用法。上面的代码将输出：

Studying [1, 2, 3] I found these even numbers ([0, 2]) among [1, 2, 3] Studying [6, 5, 4] I found these even numbers ([0, 6, 4]) among [6, 5, 4] Studying [5, 7, 9] I found these even numbers ([0]) among [5, 7, 9] This is what I found: [2, 6, 0]

Answer 5

根据我的理解，您希望迭代列表，从每个列表中获取最大的偶数，如果找不到偶数，则为0。这是你的功能：

def maximum_even_each_list_in_lol(lol):
    evens = []
    for sublist in lol:
        subevens = []
        for number in sublist:
            if (not number % 2):
                subevens.append(number)
        # As I understand you want to insert 0
        # if no even numbers were found, right?
        if not subevens:
            subevens = [0]
        evens.append(max(subevens))
    return evens

# Testing
assert maximum_even_each_list_in_lol([[1,2,3],[6,5,4],[5,7,9]]) == [2,6,0]

请务必阅读内置max功能：）

Answer 6

你去：

>>> [ max(x) if len(x)>0 else 0 for x in [ list(filter(lambda x:x%2==0,x)) for x in a ]]
[2, 6, 0]

我用lambda检查偶数，然后过滤保存值为true，如果列表的长度大于0则为max，否则为0

在列表python中查找偶数

6 个答案: