CODEWITHSUNDEEP
python
user1734291
user1734291

Reputation: 7

Print data from column and row in matrix

Suppose i have a matrix like this

table =  [
# grid: 4 by 9
['A','B','C','D'],
['E','F','G','H'],
['I','J','K','L'],
['M','N','O','P'],
['Q','R','S','T'],
['U','V','W','X'],
['Y','Z','1','2'],
['3','4','5','5'],
['7','8','9','0'],
]

If i want to print the the string thats two down on the third column(2x,3y) resulting in G. Or something along the lines. How do i tell python that it should be a grid? And how do i return list information, the table.find(something) did not work (saying table has no find attribute) Im fairly new to python. I have searched the internet, with not much help..

edit: I must be doing something wrong?

table =  [
# grid: 4 by 9
# 1   2   3   4  
['A','B','C','D'],#1
['E','F','G','H'],#2
['I','J','K','L'],#3
['M','N','O','P'],#4
['Q','R','S','T'],#5
['U','V','W','X'],#6
['Y','Z','1','2'],#7
['3','4','5','5'],#8
['7','8','9','0'],#9
]
print table[1][2], table[4][3]

Prints O and T. O is right, but T is not, thats row 5 isnt it?'

I'm trying to write a text positional encryption algorithm with text matrixes, like one of the famous ciphers( i cant remember the name of).

I want to apply the said printing of each letter to the text that is caught by raw_input, i used dictionaries before, but i want to try this row/column method if possible, it will be much harder to break.

Upvotes: 0

Views: 14845

Answers (4)

Jon Clements
Jon Clements

Reputation: 142126

Are you referring to http://en.wikipedia.org/wiki/Vigenere_cipher ?

If you want to work with matrices, then numpy is recommended (a simple example):

>>> import numpy as np
>>> a = np.array(table)
>>> a
array([['A', 'B', 'C', 'D'],
       ['E', 'F', 'G', 'H'],
       ['I', 'J', 'K', 'L'],
       ['M', 'N', 'O', 'P'],
       ['Q', 'R', 'S', 'T'],
       ['U', 'V', 'W', 'X'],
       ['Y', 'Z', '1', '2'],
       ['3', '4', '5', '5'],
       ['7', '8', '9', '0']], 
      dtype='|S1')
>>> print a[1,2]
G
>>> np.where(a=='G')
(array([1]), array([2]))

There's also an oft over looked string method that can be used to substitute text (however you decide to do it)...

>>> from string import maketrans
>>> trans = maketrans('AB', 'XY') # A->X, B->Y, everything else unchanged
>>> 'ABC'.translate(trans)
'XYC'

Upvotes: 1

root
root

Reputation: 80346

List indexing starts at zero, so for example a fourth element in a list has index 3. You can define a helper function to get items/columns by their "actual position".

def column(matrix, i):
    return [row[i-1] for row in matrix]
column(table,2)

Out[15]:
['B', 'F', 'J', 'N', 'R', 'V', 'Z', '4', '8']

def getitem(matrix,row,column):
    return matrix[row-1][column-1]
getitem(table,2,3)

Out[16]:
'G'

As for your edit, table[1][2] should print G, not O and table[4][3] rightly returns T.

Upvotes: 1

raton
raton

Reputation: 428

table =  [
['A','B','C','D'],
['E','F','G','H'],
['I','J','K','L'],
['M','N','O','P'],
['Q','R','S','T'],
['U','V','W','X'],
['Y','Z','1','2'],
['3','4','5','5'],
['7','8','9','0'],
]
# grid 4 by 9, 4 column, 9 row
rownum=3
colnum=2
print(table[rownum-1][colnum-1])

Upvotes: 1

Amber
Amber

Reputation: 526573

table[1][2] would give the value in the second row, third column (since indices start at 0).

More specifically, what you're specifying is a list of lists, so table[1] would resolve to ['E','F','G','H'] (the second item in the overall list), and then taking the third element of that with [2] would give you 'G'.

Upvotes: 2

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