topic Re: determining maximum cell from a Numpy array in Python Questions

determining maximum cell from a Numpy array

BarbaraLokes — Fri, 07 Dec 2012 07:12:00 GMT

hello

i have a large numpy array and i would like to write a python script for assigning zero (0) to every maximum cell in every four adjacent cells. For example, see figure below:

[ATTACH=CONFIG]19775[/ATTACH]

Any help would be very much appreciated, thanks in advance!

Re: determining maximum cell from a Numpy array

AndrewChapkowski — Sat, 11 Dec 2021 09:04:59 GMT

You can find a value positions by doing the following:

   itemindex=numpy.where(array==item)

Then change your values.

You can find the max value by doing the following:

>>> from numpy import *
>>> a = array([10,20,30])
>>> a.max()
30
>>> a = array([[10,50,30],[60,20,40]])
>>> a.max()
60

Hope this helps. You can find more information about numpy by going to the scipy.org site.

Re: determining maximum cell from a Numpy array

RaphaelR — Sat, 11 Dec 2021 09:05:03 GMT

tried this with a sample 6x6 grid. i´d really like to know if there´s a better way (i´m sure there is) using more numpy/scipy (tried that at first but couldn´t really get it working).
anyways...
in:

[[  5.4   7.5   2.2   8.5   8.6   7.5]
 [  7.7   3.5   1.4   9.6   8.5   5.5]
 [  5.2   6.1   8.6   6.7   4.3   6.8]
 [  9.3   4.5   2.7   3.6   6.7   4.5]
 [  1.2   2.3   7.2   6.3   2.2   2. ]
 [  1.3   2.  -99.    4.  -99.    1.2]]

nrows=6
ncols=6
for row in range(0, nrows -1, 1):
    for col in range(0, ncols -1, 1):
        # current 2x2 subgrid        
        curgrid = {grid[row,col]:(row,col), grid[row, col+1]:(row, col+1),\
                   grid[row+1,col]:(row+1,col), grid[row+1, col+1]:(row+1, col+1)}
        # set max of current subgrid in the totalgrid to 0
        grid[curgrid[max(curgrid)]] = 0

out:

[[  5.4   0.    2.2   8.5   0.    7.5]
 [  0.    3.5   1.4   0.    0.    5.5]
 [  5.2   0.    0.    0.    0.    0. ]
 [  0.    0.    2.7   0.    0.    0. ]
 [  1.2   0.    0.    0.    0.    0. ]
 [  1.3   0.  -99.    0.  -99.    0. ]]

Re: determining maximum cell from a Numpy array

AndrewChapkowski — Tue, 11 Dec 2012 14:33:16 GMT

Your list syntax is incorrect. You need to use commas between values.

You can find out about type formatting at python.org.

Thanks

Andrew

Re: determining maximum cell from a Numpy array

RaphaelR — Sat, 11 Dec 2021 09:05:07 GMT

the input is an array

print type(grid)
<type 'numpy.ndarray'>

Re: determining maximum cell from a Numpy array

AndrewChapkowski — Wed, 12 Dec 2012 09:18:37 GMT

Try putting commas after each number.

My code worked then.

Re: determining maximum cell from a Numpy array

RaphaelR — Wed, 12 Dec 2012 11:28:50 GMT

the code works for me as well.
i just said that i would also be very interested in a more/only numpy-based approach.