[Numpy-discussion] need a better way to fill a grid

[John]

I know we're not supposed to 'broadcast' thanks, but Thanks! This
works much more efficiently!

On Mon, Jan 24, 2011 at 3:50 PM, David Huard <david.huard at gmail.com> wrote:
> Hi John,
>
> Since you have a regular grid, you should be able to find the x and y
> indices without np.where, ie something like
>
> I = (lon-grid.outlon0 / grid.dx).astype(int)
> J = (lat-grid.outlat0 / grid.dy).astype(int)
>
> for i, j, e in zip(I, J, emissions):
>    Z[i,j] += e
>
>
> David
>
> On Mon, Jan 24, 2011 at 8:53 AM, John <washakie at gmail.com> wrote:
>> Hello,
>>
>> I'm trying to cycle over some vectors (lat,lon,emissions) of
>> irregularly spaced lat/lon spots, and values. I need to sum the values
>> each contributing to grid on a regular lat lon grid.
>>
>> This is what I have presently, but it is too slow. Is there a more
>> efficient way to do this? I would prefer not to create an external
>> module (f2py, cython) unless there is really no way to make this more
>> efficient... it's the looping through the grid I guess that takes so
>> long.
>>
>> Thanks,
>> john
>>
>>
>>
>>    def grid_emissions(lon,lat,emissions,grid.dx, grid.dy,
>> grid.outlat0, grid.outlon0, grid.nxmax, grid.nymax):
>>        """ sample the emissions into a grid to fold into model output
>>        """
>>
>>        dx = grid.dxout
>>        dy = grid.dyout
>>
>>        # Generate a regular grid to fill with the sum of emissions
>>        xi = np.linspace(grid.outlon0,
>> grid.outlon0+(grid.nxmax*grid.d), grid.nxmax)
>>        yi = np.linspace(grid.outlat0,
>> grid.outlat0+(grid.nymax*grid.dy), grid.nymax)
>>
>>        X, Y = np.meshgrid(yi, xi)
>>        Z = np.zeros(X.shape)
>>
>>        for i,x in enumerate(xi):
>>            for j,y in enumerate(yi):
>>                Z[i,j] = np.sum( emissions[\
>>                         np.where(((lat>y-dy) & (lat<y+dy)) &
>> ((lon>x-dx) & (lon<x+dx)))[0]])
>>
>>        return Z
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