Programming Forums > Script Programming > Python

DaWei · Jul 25th, 2006, 3:33 PM

What would be your Pythonic solution for rotating a 3x3 grid counterclockwise by 90 degrees?

MBirchmeier · Jul 25th, 2006, 4:08 PM

from a strictly code based solution I'd do something like

grid=[[grid[0][2],[grid[1][2],[grid[2][2]],[grid[0][1],[grid[1][1],[grid[2][1]],[grid[0][0],[grid[1][0],[grid[2][0]]]

I dunno about a more programatic solution though.

-MBirchmeier

titaniumdecoy · Jul 25th, 2006, 7:18 PM

I know this isn't the Pythonic answer you're looking for, but it's an improvement:

(Toggle Plain Text)

for i in xrange(len(grid)):
    for j in xrange(len(grid)):
        new_grid[i][j] = grid[j][abs(len(grid) - 1 - i)]

Sane · Jul 25th, 2006, 9:42 PM

Pythonic? That would be a simple implementation of an inverse function, using list comprehensions. We will need to count down from the max value, since Python counts backwards (if we are considering the cartegean plane).

(Toggle Plain Text)

print [[grid[y][l-x] for y in range(h)] for x in range(w)]

Where w is the width, h is the height, and l = w-1 (defined for efficiency purposes).

titaniumdecoy · Jul 25th, 2006, 9:59 PM

I think the idea is to create a new grid (or modify the original grid), rather than just print the values; this is a little harder. But I may be mistaken.

Sane · Jul 25th, 2006, 10:09 PM

Err... am I missing something? @_@ ...

Chapter 1 of the Python tutorial?? You can replace "print" with "grid =" ...

...

---

(Assignment takes place after calculation. It doesn't keep assigning as it's going, so you don't need to worry about that.

)

titaniumdecoy · Jul 25th, 2006, 10:55 PM

Oh, sorry, missed that.

In that case, that's probably the best way to do it. It's simple, concise, and easy to read. Although I wouldn't define a separate variable for w-1, but that's just my preference.

Sane · Jul 25th, 2006, 11:21 PM

Well, it's usually a poor choice to blatantly disregard simple optimization... especially when all it calls for is swapping a calculation for a variable.

I know it barely makes any difference at all, but it would if say, w-1, was instead a function call. I realise in that case, you would have done it differently, but it's always best to be consistent with your style and make good habits.

Although I am being hypocritical, since, in respect to commenting ... I would never be consistent and comment every single program I make.

andro · Jul 26th, 2006, 12:41 AM

I would use matrix math and apply a transformation matrix to it.

DaWei · Jul 26th, 2006, 7:29 AM

Quote:

I would use matrix math and apply a transformation matrix to it.

Why? Example?

Jul 25th, 2006, 3:33 PM	#1
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Next: grid rotation What would be your Pythonic solution for rotating a 3x3 grid counterclockwise by 90 degrees? __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Jul 25th, 2006, 4:08 PM	#2
MBirchmeier Hobbyist Programmer Join Date: Oct 2005 Posts: 211 Rep Power: 3	from a strictly code based solution I'd do something like (Toggle Plain Text) grid=[[grid[0][2],[grid[1][2],[grid[2][2]],[grid[0][1],[grid[1][1],[grid[2][1]],[grid[0][0],[grid[1][0],[grid[2][0]]] grid=[[grid[0][2],[grid[1][2],[grid[2][2]],[grid[0][1],[grid[1][1],[grid[2][1]],[grid[0][0],[grid[1][0],[grid[2][0]]] I dunno about a more programatic solution though. -MBirchmeier

Jul 25th, 2006, 7:18 PM	#3
titaniumdecoy Expert Programmer Join Date: Nov 2005 Posts: 836 Rep Power: 3	I know this isn't the Pythonic answer you're looking for, but it's an improvement: (Toggle Plain Text) for i in xrange(len(grid)): for j in xrange(len(grid)): new_grid[i][j] = grid[j][abs(len(grid) - 1 - i)] for i in xrange(len(grid)): for j in xrange(len(grid)): new_grid[i][j] = grid[j][abs(len(grid) - 1 - i)]

Jul 25th, 2006, 9:42 PM	#4
Sane Programming Guru Join Date: Apr 2005 Posts: 1,791 Rep Power: 5	Pythonic? That would be a simple implementation of an inverse function, using list comprehensions. We will need to count down from the max value, since Python counts backwards (if we are considering the cartegean plane). (Toggle Plain Text) print [[grid[y][l-x] for y in range(h)] for x in range(w)] print [[grid[y][l-x] for y in range(h)] for x in range(w)] Where w is the width, h is the height, and l = w-1 (defined for efficiency purposes).

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Jul 25th, 2006, 9:59 PM	#5
titaniumdecoy Expert Programmer Join Date: Nov 2005 Posts: 836 Rep Power: 3	I think the idea is to create a new grid (or modify the original grid), rather than just print the values; this is a little harder. But I may be mistaken.

Jul 25th, 2006, 10:09 PM	#6
Sane Programming Guru Join Date: Apr 2005 Posts: 1,791 Rep Power: 5	Err... am I missing something? @_@ ... Chapter 1 of the Python tutorial?? You can replace "print" with "grid =" ... ... --- (Assignment takes place after calculation. It doesn't keep assigning as it's going, so you don't need to worry about that. )

Jul 25th, 2006, 10:55 PM	#7
titaniumdecoy Expert Programmer Join Date: Nov 2005 Posts: 836 Rep Power: 3	Oh, sorry, missed that. In that case, that's probably the best way to do it. It's simple, concise, and easy to read. Although I wouldn't define a separate variable for w-1, but that's just my preference.

Jul 25th, 2006, 11:21 PM	#8
Sane Programming Guru Join Date: Apr 2005 Posts: 1,791 Rep Power: 5	Well, it's usually a poor choice to blatantly disregard simple optimization... especially when all it calls for is swapping a calculation for a variable. I know it barely makes any difference at all, but it would if say, w-1, was instead a function call. I realise in that case, you would have done it differently, but it's always best to be consistent with your style and make good habits. Although I am being hypocritical, since, in respect to commenting ... I would never be consistent and comment every single program I make.

Jul 26th, 2006, 12:41 AM	#9
andro Professional Programmer Join Date: Oct 2005 Location: California Posts: 290 Rep Power: 3	I would use matrix math and apply a transformation matrix to it.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
[Python] Grid encryptor	Jessehk	Show Off Your Open Source Projects	7	Nov 29th, 2007 7:11 PM
Distance between 2 grid references	Oddball	Show Off Your Open Source Projects	7	Mar 12th, 2006 2:52 PM
easiest way to represent a grid?	keweedsmo	C++	4	Feb 10th, 2006 6:03 PM
Little off-topic... Grid coordinate handling	CodeCaster	C++	13	Jul 4th, 2005 7:07 AM
Need assistance with program	DJ_Mittens	C++	4	Apr 20th, 2005 7:48 AM

Programming Forums > Script Programming > Python

Next: grid rotation