Slicing using np.array but getting IndexError - numpy

Question

I've been getting IndexError: too many indices for array at the first line of the squares.append and the other posts on IndexError just seemed a little too confusing, so it would be great if there can be a simple explanation on why I'm getting this!
def check_squares(grid):
squares=[]
count_dic={}
count_dic[0]=0
for num in range(1,10):
count_dic[num]=0
squares.append(list(((np.array(grid)[:3,:3]).reshape(-1))))
squares.append(list(((np.array(grid)[:3,3:6]).reshape(-1))))
squares.append(list(((np.array(grid)[:3,6:9]).reshape(-1))))
squares.append(list(((np.array(grid)[3:6,:3]).reshape(-1))))
squares.append(list(((np.array(grid)[3:6,3:6]).reshape(-1))))
squares.append(list(((np.array(grid)[3:6,6:9]).reshape(-1))))
squares.append(list(((np.array(grid)[6:9,:3]).reshape(-1))))
squares.append(list(((np.array(grid)[6:9,3:6]).reshape(-1))))
squares.append(list(((np.array(grid)[6:9,6:9]).reshape(-1))))
for lst in squares:
for i in lst:
count_dic[i]+=1
count_dic[0]=0
if (all(value <=1 for value in count_dic.values()))==True:
for num in range(1,10):
count_dic[num]=0
else:
return False
return True
ill_formed = [[5,3,4,6,7,8,9,1,2],
[6,7,2,1,9,5,3,4,8],
[1,9,8,3,4,2,5,6,7],
[8,5,9,7,6,1,4,2,3],
[4,2,6,8,5,3,7,9], # <---
[7,1,3,9,2,4,8,5,6],
[9,6,1,5,3,7,2,8,4],
[2,8,7,4,1,9,6,3,5],
[3,4,5,2,8,6,1,7,9]]
valid = [[5,3,4,6,7,8,9,1,2],
[6,7,2,1,9,5,3,4,8],
[1,9,8,3,4,2,5,6,7],
[8,5,9,7,6,1,4,2,3],
[4,2,6,8,5,3,7,9,1],
[7,1,3,9,2,4,8,5,6],
[9,6,1,5,3,7,2,8,4],
[2,8,7,4,1,9,6,3,5],
[3,4,5,2,8,6,1,7,9]]
print(check_squares(valid))
print (check_squares(ill-formed))
Error message: in check_squares
squares.append(list(((np.array(grid)[:3,:3]).reshape(-1))))
IndexError: too many indices for array
traceback.print_stack()
File "C:\ProgramData\Anaconda3\lib\site-packages\spyder\utils\ipython\start_kernel.py", line 245, in <module>
main()
File "C:\ProgramData\Anaconda3\lib\site-packages\spyder\utils\ipython\start_kernel.py", line 241, in main
kernel.start()
File "C:\ProgramData\Anaconda3\lib\site-packages\ipykernel\kernelapp.py", line 477, in start
ioloop.IOLoop.instance().start()
File "C:\ProgramData\Anaconda3\lib\site-packages\zmq\eventloop\ioloop.py", line 177, in start
super(ZMQIOLoop, self).start()
File "C:\ProgramData\Anaconda3\lib\site-packages\tornado\ioloop.py", line 888, in start
handler_func(fd_obj, events)
File "C:\ProgramData\Anaconda3\lib\site-packages\tornado\stack_context.py", line 277, in null_wrapper
return fn(*args, **kwargs)
File "C:\ProgramData\Anaconda3\lib\site-packages\zmq\eventloop\zmqstream.py", line 440, in _handle_events
self._handle_recv()
File "C:\ProgramData\Anaconda3\lib\site-packages\zmq\eventloop\zmqstream.py", line 472, in _handle_recv
self._run_callback(callback, msg)
File "C:\ProgramData\Anaconda3\lib\site-packages\zmq\eventloop\zmqstream.py", line 414, in _run_callback
callback(*args, **kwargs)
File "C:\ProgramData\Anaconda3\lib\site-packages\tornado\stack_context.py", line 277, in null_wrapper
return fn(*args, **kwargs)
File "C:\ProgramData\Anaconda3\lib\site-packages\ipykernel\kernelbase.py", line 283, in dispatcher
return self.dispatch_shell(stream, msg)
File "C:\ProgramData\Anaconda3\lib\site-packages\ipykernel\kernelbase.py", line 235, in dispatch_shell
handler(stream, idents, msg)
File "C:\ProgramData\Anaconda3\lib\site-packages\ipykernel\kernelbase.py", line 399, in execute_request
user_expressions, allow_stdin)
File "C:\ProgramData\Anaconda3\lib\site-packages\ipykernel\ipkernel.py", line 196, in do_execute
res = shell.run_cell(code, store_history=store_history, silent=silent)
File "C:\ProgramData\Anaconda3\lib\site-packages\ipykernel\zmqshell.py", line 533, in run_cell
return super(ZMQInteractiveShell, self).run_cell(*args, **kwargs)
File "C:\ProgramData\Anaconda3\lib\site-packages\IPython\core\interactiveshell.py", line 2698, in run_cell
interactivity=interactivity, compiler=compiler, result=result)
File "C:\ProgramData\Anaconda3\lib\site-packages\IPython\core\interactiveshell.py", line 2808, in run_ast_nodes
if self.run_code(code, result):
File "C:\ProgramData\Anaconda3\lib\site-packages\IPython\core\interactiveshell.py", line 2862, in run_code
exec(code_obj, self.user_global_ns, self.user_ns)
File "<ipython-input-9-e4a4d877ed6a>", line 1, in <module>
traceback.print_stack()
Really appreciate any help, thanks!

Answer 1

Here's my solution - you can try improving upon it.
def check_squares(grid):
grid = np.array(grid)
for i in grid:
unique , counts = (np.unique(i, return_counts=True))
#print(unique, counts)
if len(counts)<9:
return(False)
for i in np.split(grid,3):
for t in (np.hsplit(i,3)):
unique1 , counts1 = np.unique(t, return_counts=True)
#print(unique1,counts1)
if len(counts1)<9:
return(False)
return (True)
Learn about numpy array splits and slicing. Do not use array reshape half a dozen times to obtain your 3*3 sub-array. I have used np split and np.hsplit
Perform all your matrix operations in the numpy space.
you can use np.unique with return counts set as True to obtain how many unique numbers are present in your input and how many times this has occurred. You can use this obtain to identify if your sub-array has repeating characters.
Suggestions - currently you are not checking if your input is valid -eg: if your input has 12 in the sudoku grid , above code does not handle it.
you were also not checking if your rows and columns are valid sudoku columns. I have handled the row situation - i'll leave the job of checking if each column is a valid sudoku column upto you
Check it out. Happy learning!