Matrix Transpose in Python

Question

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

User · Answer

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

User · Answer

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

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Python 2    gt  gt  gt  theArray      a   b   c     d   e   f     g   h   i     gt  gt  gt  zip  theArray     a    d    g      b    e    h      c    f    i      Python 3    gt  gt  gt    zip  theArray      a    d    g      b    e    h      c    f    i

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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

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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

User · Answer

If your rows are not equal you can also use map    gt  gt  gt  uneven      a   b   c     d   e     g   h   i     gt  gt  gt  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   gt  gt  gt  import itertools  gt  gt  gt  uneven      a   b   c     d   e     g   h   i     gt  gt  gt  list itertools zip longest  uneven      a    d    g      b    e    h      c   None   i

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you can try this with list comprehension like the following  matrix      a   b   c     d   e   f     g   h   i    n   len matrix  transpose     row i  for row in matrix  for i in range n   print  transpose

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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

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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

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gt  gt  gt  theArray      a   b   c     d   e   f     g   h   i     gt  gt  gt   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

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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

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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

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You may do it simply using python comprehension   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

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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

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Much easier with numpy    gt  gt  gt  arr   np array   1 2 3   4 5 6   7 8 9     gt  gt  gt  arr array   1  2  3           4  5  6           7  8  9     gt  gt  gt  arr T array   1  4  7           2  5  8           3  6  9     gt  gt  gt  theArray   np array    a   b   c     d   e   f     g   h   i      gt  gt  gt  theArray  array    a    b    c             d    e    f             g    h    i            dtype   S1    gt  gt  gt  theArray T array    a    d    g             b    e    h             c    f    i            dtype   S1

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x000D   x000D  def transpose m   x000D      return list map list list zip  m      x000D   x000D   x000D     This function will return the transpose

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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

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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

[python] Matrix Transpose in Python

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