如何獲取列表中的第一個值作爲單獨的列表？

Question

如何獲取列表中的第一個值作爲單獨的列表？

例如：

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

的結果應該爲：

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