问题
I am trying to create a matrix transpose function for python but I can't seem to make it work. Say I have
theArray = [['a','b','c'],['d','e','f'],['g','h','i']]
and I want my function to come up with
newArray = [['a','d','g'],['b','e','h'],['c', 'f', 'i']]
So in other words, if I were to print this 2D array as columns and rows I would like the rows to turn into columns and columns into rows.
I made this so far but it doesn't work
def matrixTranspose(anArray):
transposed = [None]*len(anArray[0])
for t in range(len(anArray)):
for tt in range(len(anArray[t])):
transposed[t] = [None]*len(anArray)
transposed[t][tt] = anArray[tt][t]
print transposed
回答1:
Python 2:
>>> theArray = [['a','b','c'],['d','e','f'],['g','h','i']]
>>> zip(*theArray)
[('a', 'd', 'g'), ('b', 'e', 'h'), ('c', 'f', 'i')]
Python 3:
>>> [*zip(*theArray)]
[('a', 'd', 'g'), ('b', 'e', 'h'), ('c', 'f', 'i')]
回答2:
>>> theArray = [['a','b','c'],['d','e','f'],['g','h','i']]
>>> [list(i) for i in zip(*theArray)]
[['a', 'd', 'g'], ['b', 'e', 'h'], ['c', 'f', 'i']]
the list generator creates a new 2d array with list items instead of tuples.
回答3:
If your rows are not equal you can also use map:
>>> uneven = [['a','b','c'],['d','e'],['g','h','i']]
>>> map(None,*uneven)
[('a', 'd', 'g'), ('b', 'e', 'h'), ('c', None, 'i')]
Edit: In Python 3 the functionality of map changed, itertools.zip_longest can be used instead:
Source: What’s New In Python 3.0
>>> import itertools
>>> uneven = [['a','b','c'],['d','e'],['g','h','i']]
>>> list(itertools.zip_longest(*uneven))
[('a', 'd', 'g'), ('b', 'e', 'h'), ('c', None, 'i')]
回答4:
Much easier with numpy:
>>> arr = np.array([[1,2,3],[4,5,6],[7,8,9]])
>>> arr
array([[1, 2, 3],
[4, 5, 6],
[7, 8, 9]])
>>> arr.T
array([[1, 4, 7],
[2, 5, 8],
[3, 6, 9]])
>>> theArray = np.array([['a','b','c'],['d','e','f'],['g','h','i']])
>>> theArray
array([['a', 'b', 'c'],
['d', 'e', 'f'],
['g', 'h', 'i']],
dtype='|S1')
>>> theArray.T
array([['a', 'd', 'g'],
['b', 'e', 'h'],
['c', 'f', 'i']],
dtype='|S1')
回答5:
The problem with your original code was that you initialized transpose[t] at every element, rather than just once per row:
def matrixTranspose(anArray):
transposed = [None]*len(anArray[0])
for t in range(len(anArray)):
transposed[t] = [None]*len(anArray)
for tt in range(len(anArray[t])):
transposed[t][tt] = anArray[tt][t]
print transposed
This works, though there are more Pythonic ways to accomplish the same things, including @J.F.'s zip application.
回答6:
To complete J.F. Sebastian's answer, if you have a list of lists with different lengths, check out this great post from ActiveState. In short:
The built-in function zip does a similar job, but truncates the result to the length of the shortest list, so some elements from the original data may be lost afterwards.
To handle list of lists with different lengths, use:
def transposed(lists):
if not lists: return []
return map(lambda *row: list(row), *lists)
def transposed2(lists, defval=0):
if not lists: return []
return map(lambda *row: [elem or defval for elem in row], *lists)
回答7:
The "best" answer has already been submitted, but I thought I would add that you can use nested list comprehensions, as seen in the Python Tutorial.
Here is how you could get a transposed array:
def matrixTranspose( matrix ):
if not matrix: return []
return [ [ row[ i ] for row in matrix ] for i in range( len( matrix[ 0 ] ) ) ]
回答8:
This one will preserve rectangular shape, so that subsequent transposes will get the right result:
import itertools
def transpose(list_of_lists):
return list(itertools.izip_longest(*list_of_lists,fillvalue=' '))
回答9:
If you want to transpose a matrix like A = np.array([[1,2],[3,4]]), then you can simply use A.T, but for a vector like a = [1,2], a.T does not return a transpose! and you need to use a.reshape(-1, 1), as below
import numpy as np
a = np.array([1,2])
print('a.T not transposing Python!\n','a = ',a,'\n','a.T = ', a.T)
print('Transpose of vector a is: \n',a.reshape(-1, 1))
A = np.array([[1,2],[3,4]])
print('Transpose of matrix A is: \n',A.T)
回答10:
def matrixTranspose(anArray):
transposed = [None]*len(anArray[0])
for i in range(len(transposed)):
transposed[i] = [None]*len(transposed)
for t in range(len(anArray)):
for tt in range(len(anArray[t])):
transposed[t][tt] = anArray[tt][t]
return transposed
theArray = [['a','b','c'],['d','e','f'],['g','h','i']]
print matrixTranspose(theArray)
回答11:
python 3 easy way with Comprehensions
arr = [['a','b','c'],['d','e','f'],['g','h','i']]
transpose = [[arr[y][x] for y in range(len(arr))] for x in range(len(arr[0]))]
回答12:
#generate matrix
matrix=[]
m=input('enter number of rows, m = ')
n=input('enter number of columns, n = ')
for i in range(m):
matrix.append([])
for j in range(n):
elem=input('enter element: ')
matrix[i].append(elem)
#print matrix
for i in range(m):
for j in range(n):
print matrix[i][j],
print '\n'
#generate transpose
transpose=[]
for j in range(n):
transpose.append([])
for i in range (m):
ent=matrix[i][j]
transpose[j].append(ent)
#print transpose
for i in range (n):
for j in range (m):
print transpose[i][j],
print '\n'
回答13:
a=[]
def showmatrix (a,m,n):
for i in range (m):
for j in range (n):
k=int(input("enter the number")
a.append(k)
print (a[i][j]),
print('\t')
def showtranspose(a,m,n):
for j in range(n):
for i in range(m):
print(a[i][j]),
print('\t')
a=((89,45,50),(130,120,40),(69,79,57),(78,4,8))
print("given matrix of order 4x3 is :")
showmatrix(a,4,3)
print("Transpose matrix is:")
showtranspose(a,4,3)
回答14:
def transpose(matrix):
x=0
trans=[]
b=len(matrix[0])
while b!=0:
trans.append([])
b-=1
for list in matrix:
for element in list:
trans[x].append(element)
x+=1
x=0
return trans
回答15:
def transpose(matrix):
listOfLists = []
for row in range(len(matrix[0])):
colList = []
for col in range(len(matrix)):
colList.append(matrix[col][row])
listOfLists.append(colList)
return listOfLists
回答16:
`
def transpose(m):
return(list(map(list,list(zip(*m)))))`This function will return the transpose
回答17:
Python Program to transpose matrix:
row,col = map(int,input().split())
matrix = list()
for i in range(row):
r = list(map(int,input().split()))
matrix.append(r)
trans = [[0 for y in range(row)]for x in range(col)]
for i in range(len(matrix[0])):
for j in range(len(matrix)):
trans[i][j] = matrix[j][i]
for i in range(len(trans)):
for j in range(len(trans[0])):
print(trans[i][j],end=' ')
print(' ')
来源：https://stackoverflow.com/questions/4937491/matrix-transpose-in-python