如何将列表列表中的第一个值作为单独的列表？

Question

如何将列表列表中的第一个值作为单独的列表？

例如：

A =  [ [[1,4.9], [2,90],[3,8]], [[2,34],[4,78],[9,10]], [[1,90],[3,100]] ]

结果应为：

B = [ [1,2,3],[2,4,9],[1,3] ]

Answer 1

In [99]: A =  [ [[1,4.9], [2,90],[3,8]], [[2,34],[4,78],[9,10]], [[1,90],[3,100]] ]

In [100]: [[item[0] for item in subl] for subl in A]
Out[100]: [[1, 2, 3], [2, 4, 9], [1, 3]]

Answer 2

[map(None,*k)[0] for k in A]
[(1,2,3),(2,4,9),(1,3)]

Answer 3

def getFirstValues(A):
    B = list()
    for eachListofList in A:
        currentList= list()
        for eachList in eachListofList:
            currentList.append(eachList[0])
        B.append(currentList)
     return B