How to input matrix 2D list in Python

Question

I tried to create this code to input an m by n matrix  I intended to input   1 2 3   4 5 6   but the code yields   4 5 6   4 5 6   Same things happen when I input other m by n matrix  the code yields an m by n matrix whose rows are identical    Perhaps you can help me to find what is wrong with my code   m   int input  number of rows  m       n   int input  number of columns  n       matrix       columns        initialize the number of rows for i in range 0 m     matrix     0    initialize the number of columns for j in range  0 n     columns     0    initialize the matrix for i in range  0 m     matrix i    columns for i in range  0 m     for j in range  0 n       print   entry in row    i 1   column    j 1      matrix i  j    int input    print  matrix

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a      b       m input  enter no of rows     n input  enter no of coloumns      for i in range n        a           for j in range m            a append input         b append a    Input   1 2 3 4 5 6 7 8 9  Output       1    2    3       4    5    6       7    8    9

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The problem is on the initialization step   for i in range  0 m     matrix i    columns   This code actually makes every row of your matrix refer to the same columns object  If any item in any column changes - every other column will change    gt  gt  gt  for i in range  0 m           matrix i    columns       gt  gt  gt  matrix   0  0  0    0  0  0    gt  gt  gt  matrix 1  1    2  gt  gt  gt  matrix   0  2  0    0  2  0     You can initialize your matrix in a nested loop  like this   matrix      for i in range 0 m       matrix append         for j in range 0 n           matrix i  append 0    or  in a one-liner by using list comprehension   matrix     0 for j in range n   for i in range m     or   matrix    x    for x in   0  n  m    See also    How to initialize a two-dimensional array in Python    Hope that helps

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Creating matrix with prepopulated numbers can be done with list comprehension  It may be hard to read but it gets job done   rows   int input  Number of rows      cols   int input  Number of columns      matrix     i   cols   j for i in range 1  cols   1   for j in range rows     with 2 rows and 3 columns matrix will be   1  2  3    4  5  6    with 3 rows and 2 columns matrix will be   1  2    3  4    5  6   etc

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rows  columns   list map int input   split      input no  of row and column b    for i in range rows       a list map int input   split         b append a  print b    input  2 3 1 2 3 4 5 6   output    1  2  3    4  5  6

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If you want to take n lines of input where each line contains m space separated integers like   1 2 3 4 5 6  7 8 9    Then you can use    a       declaration  for i in range 0 n       where n is the no  of lines you want   a append  int j  for j in input   split         for taking m space separated integers as input   Then print whatever you want like for the above input    print a 1  1      O P would be 5 for 0 based indexing

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you can accept a 2D list in python this way      simply  arr2d     j for j in input   strip    for i in range n      n is no of rows   for characters  n   int input   strip    m   int input   strip    a     0  n for   in range m   for i in range n       a i    list input   strip    print a    or  n   int input   strip    n   int input   strip    a      for i in range n       a i  append list input   strip     print a    for numbers  n   int input   strip    m   int input   strip    a     0  n for   in range m   for i in range n       a i     int j  for j in input   strip   split       print a    where n is no of elements in columns while m is no of elements in a row   In pythonic way  this will create a list of list

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This code takes number of row and column from user then takes elements and displays as a matrix   m   int input  number of rows  m       n   int input  number of columns  n       a    for i in range 1 m 1     b        print   0  Row  format i     for j in range 1 n 1       b append int input   0  Column     format j       a append b  print a

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If the input is formatted like this     1 2 3 4 5 6 7 8 9   a one liner can be used    mat    list map int input   split     for i in range row

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m n map int input   split      m - number of rows  n - number of columns   matrix     int j  for j in input   split    n   for i in range m    for i in matrix print i

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Apart from the accepted answer  you can also initialise your rows in the following manner -  matrix i     0  n  Therefore  the following piece of code will work -   m   int input  number of rows  m       n   int input  number of columns  n       matrix        initialize the number of rows for i in range 0 m       matrix     0    initialize the matrix for i in range  0 m       matrix i     0  n for i in range  0 m       for j in range  0 n           print   entry in row    i 1   column    j 1          matrix i  j    int input    print  matrix

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You can make any dimension of list list    n  int input    for i in range 0 n         num   input       list append input   split    print list   output

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If your matrix is given in row manner like below  where size is s s here s 5  5 31 100 65 12 18 10 13 47 157 6 100 113 174 11 33 88 124 41 20 140 99 32 111 41 20  then you can use this  s int input    b list map int input   split     arr   b j s i  for j in range s  for i in range s     your matrix will be  arr

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a b       n int input  Provide me size of squre matrix row  column       for i in range n      for j in range n         b append int input         a append b      print  Here your    column     format i 1 a       b    for m in range n       print a m     works perfectly

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no of rows   3    For n by n  and even works for n by m but just give no of rows matrix     int j  for j in input   split    for i in range n   print matrix

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I used numpy library and it works fine for me  Its just a single line and easy to understand  The input needs to be in a single size separated by space and the reshape converts the list into shape you want  Here  2 2  resizes the list of 4 elements into 2 2 matrix   Be careful in giving equal number of elements in the input corresponding to the dimension of the matrix   import numpy as np a np array list map int input   strip   split         reshape 2 2   print a    Input  array   1  2           3  4      Output

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row list map int input   split      input no  of row and column b    for i in range 0 row 0        print  value of i    i      a list map int input   split         print a      b append a  print b  print row    Output   2 3  value of i 0 1 2 4 5  1  2  4  5  value of i   1 2 4 5 6  2  4  5  6    1  2  4  5    2  4  5  6    2  3    Note  this code in case of control it only control no  Of rows but we can enter any number of column we want i e row 0  2 so be careful  This is not the code where you can control no of columns

[python] How to input matrix (2D list) in Python?

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