Can I save data as a three-column matrix?

Question

I need to store values of a function of x and y defined as f[x_, y_] := Sin[Pi*x/3]*Sin[Pi*y/3] at the following points xval = {0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15};, same for y.

I need it to be a matrix of dimensions {961,3}, being the first two columns the values of X and Y and the third, the value of f(x,y) at said points.

I have tried to use outer as Outer[f, xval, yval];, but it provides a result whose dimensions are {31, 31}. Is there a way to reshape the dimensions or an alternative to Outer which allows for the data to be stored as I need?

Answer 1

another alternative is to use meshgrid

ClearAll[f, x, y];
f[x_, y_] := Sin[Pi*x/3]*Sin[Pi*y/3];
meshgrid[x_List, y_List] := {ConstantArray[x, Length[x]], 
  Transpose@ConstantArray[y, Length[y]]}
{xx, yy} = meshgrid[Range[0, 15, .5], Range[0, 15, .5]];
u = f[xx, yy];
pts = Flatten[{xx, yy, u}, {2, 3}];

ListPlot3D[pts, PlotRange -> All, AxesLabel -> Automatic, 
 ImagePadding -> 20, Mesh -> 35, InterpolationOrder -> 2, 
 ColorFunction -> "Rainbow", Boxed -> False]

But if you really need to have them all in one matrix, then

meshgrid[x_List, y_List] := {ConstantArray[x, Length[x]], 
  Transpose@ConstantArray[y, Length[y]]}
{xx, yy} = meshgrid[Range[0, 15, .5], Range[0, 15, .5]];
x0 = Flatten[xx]; y0 = Flatten[yy];
mat = Transpose[{x0, y0, f[x0, y0]}];
Dimensions[mat]

Reference Simulate MATLAB's meshgrid function

Answer 2

Maybe this is what you want:

Map[
 X \[Function] {Indexed[X, 1], Indexed[X, 2], f[Indexed[X, 1], Indexed[X, 2]]},
 Tuples[{xval, yval}]
 ]