[Scilab-users] hist3d & density plots

[Stéphane Mottelet]

Le 10/09/2018 à 09:56, antoine.monmayrant at laas.fr a écrit :
> Hi all,
>
> I'm trying to plot the density of scatter points in (x,y).
> Basically, I have a huge Xvec and a huge Yvec of same size that 
> represents the position of a huge number of points in a 2D plane.
> I would like to get a density plot, that is given a certain grid, a 2D 
> plot representing the number of scatter points within a each cell of 
> the grid.
> In matplotib, this corresponds to functions like "hist2d" and "hexbin".
> Is there any equivalent in Scilab?
> Or do I have to calculate by hand my density matrix and then use 
> graplot or contourfill to plot my density?
> Any pointer at the least inefficient way to do this calculation is 
> more than welcome...
>
> Thank you in advance for your help,
>
>
> Antoine
>
Hello Antoine,

The most efficient at the Scilab level would be to use the incremental 
feature of "sparse":

function d=bins2d(x,y,xbins,ybins)
      n = size(x,"*");
     [ix,cx] = dsearch(x,xbins);
     [iy,cy] = dsearch(y,ybins);
     kin = find((ix>0) & (iy>0));
     d = full(sparse([ix(kin) iy(kin)], ones(kin), [size(xbins,"*")-1, 
size(ybins,"*")-1]));
end

x = rand(10000,1,'normal');
y = rand(10000,1,'normal');

--> d = bins2d(x,y,-5:5,-5:5)
  d  =

    0.   0.   0.    0.     1.      0.      0.     0.    0.   0.
    0.   0.   0.    3.     4.      4.      0.     0.    0.   0.
    0.   0.   6.    31.    82.     80.     31.    2.    0.   0.
    0.   0.   24.   183.   477.    477.    200.   25.   3.   0.
    0.   5.   68.   439.   1131.   1158.   426.   57.   4.   0.
    0.   5.   91.   485.   1168.   1220.   438.   72.   3.   0.
    0.   4.   30.   190.   470.    472.    173.   21.   3.   0.
    0.   0.   6.    30.    83.     78.     24.    2.    0.   0.
    0.   1.   0.    2.     2.      3.      3.     0.    0.   0.
    0.   0.   0.    0.     0.      0.      0.     0.    0.   0.


--> sum(d)
  ans  =

    10000.

This feature is fixed in scilab-branch-6.0:

S.

-- 
Stéphane Mottelet
Ingénieur de recherche
EA 4297 Transformations Intégrées de la Matière Renouvelable
Département Génie des Procédés Industriels
Sorbonne Universités - Université de Technologie de Compiègne
CS 60319, 60203 Compiègne cedex
Tel : +33(0)344234688
http://www.utc.fr/~mottelet