How to bin data in 3 dimensions - 3/4 done but stuck!

I'm trying to create a 3d matrix gridded as depth x longitude x time with a field of temperature, so that I can select the data based on days, or certain longitude for example. I have done this 2 dimensional, but I am stuck trying to do it 3 dimensional. Can someone help me finish the following code?

% try 3d gridding

x1 = [lonlat(:).v]; % this is longitude
x2 = [date(:).depth];
x3 = [data(:).time];
y = [data(:).temp];

x1rg = [7:0.020:9];
x2rg = [0:5:1000];
x3rg = [min(x3):12:max(x3)]; % not sure if right

for n = 2:size((prcdata_SG502.flight),2);
   n 

     if isempty(prcdata_SG502.hydrography(n).depth') == 0;

lonlat(n).v = prcdata_SG502.flight(n).trajectory_latlon_estimated(:,2)';
   end
end

good = ~isnan(x1+x2+x3+y);

[~,whichedge1] = histc(x1(good),x1rg(:)');
[~,whichedge2] = histc(x2(good),x2rg(:)');
[~,whichedge3] = histc(x3(good),x3rg(:)');

bins1 = min(max(whichedge1,1),length(x1rg)-1);
bins2 = min(max(whichedge2,1),length(x2rg)-1);
bins3 = min(max(whichedge3,1),length(x3rg)-1);

bins = (bins2-1)*(length(x1rg)-1)+bins1; % from here onwards I am really stuck!

xpos = ones(size(bins,1),1);
ns = sparse(bins,xpos,1,(length(x1rg)-1)*(length(x2rg)-1),1);
ysum = sparse(bins,xpos,y(good),(length(x1rg)-1)*(length(x2rg)-1),1);
ym = full(ysum)./(full(ns));
yb = ym(bins);
ym = reshape(ym,length(x1rg)-1,length(x2rg)-1)';

thanks, Michael

Answer 1

[Walter Roberson]

bins = (bins2-1)*(length(x1rg)-1)+bins1; % from here onwards I am really stuck!

bins = sub2ind([length(x1rg), length(x2rg), length(x3rg)], bins1, bins2, bins3);