how to sort a dataset into different group and get sum of each group?

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Genhou
Genhou 2014-1-23
回答： Walter Roberson 2014-1-24
Hi everyone,
Now I have a question on how to sort a dataset into different group and get sum of each group, which tortures me for sevral day. I hope to get help from you, and thanks.
An example of my dataset is shown below. There are 9 rows and 12 columns. This first and second rows are x, y coordinates and the third row is the correponding value of each (x ,y).
-1.986 -2.648 -3.310 -3.972 -4.634 -5.296 -5.958 -6.621 -7.283 -7.945 -8.607 -9.269 -9.931 -10.593 -11.255 -11.917 -12.579//
-4.515 -6.020 -7.525 -9.030 -10.536 -12.041 -13.546 -15.051 -16.556 -18.061 -19.566 -21.071 -22.576 -24.081 -25.586 -27.091//
0.002 0.003 0.003 0.004 0.004 0.005 0.005 0.005 0.006 0.006 0.006 0.007 0.007 0.007 0.007 0.008 0.008 0.008
-3.967 -5.289 -6.611 -7.934 -9.256 -10.578 -11.900 -13.223 -14.545 -15.867 -17.189 -18.512 -19.834 -21.156 -22.478 -23.801//
-5.372 -7.163 -8.954 -10.745 -12.536 -14.326 -16.117 -17.908 -19.699 -21.490 -23.280 -25.071 -26.862 -28.653 -30.443 -32.234//
0.001 0.002 0.002 0.003 0.003 0.003 0.004 0.004 0.004 0.005 0.005 0.005 0.005 0.005 0.005 0.006
-3.606 -4.808 -6.011 -7.213 -8.415 -9.617 -10.819 -12.021 -13.223 -14.425 -15.627 -16.829 -18.032 -19.234 -20.436 -21.638//
-2.758 -3.678 -4.597 -5.517 -6.436 -7.356 -8.275 -9.195 -10.114 -11.034 -11.953 -12.873 -13.792 -14.711 -15.631 -16.550//
0.002 0.003 0.003 0.004 0.005 0.005 0.006 0.006 0.006 0.007 0.007 0.007 0.008 0.008 0.008 0.008
I want to sort the data according to (x,y) coordinates into idfferent groups and get the sums of each group. In this case, the group can be
(-35<x<-30,-35<y<-30),(-30<x<-25,-35<y<-30),....(-5<x<0,-35<y<-30);
(-35<x<-30,-30<y<-25),(-30<x<-25,-30<y<-25),....(-5<x<0,-30<y<-25);
(-35<x<-30,-25<y<-20),(-30<x<-25,-25<y<-20),....(-5<x<0,-25<y<-20);
(-35<x<-30,-5<y< 0),(-30<x<-25,-5<y< 0),....(-5<x<0,-5<y<0)
Then get the sum of each group.
Thanks once again.
  2 个评论
Walter Roberson
Walter Roberson 2014-1-23
Is it correct that you are wanting to distribute into a rectangular grid? If so it becomes easy. Even easier if the grid boundaries are the same distance apart.
What should be done for the case that x is exactly 30? As you have used inequalities at each stage, points on the boundaries have no-where to go.
Genhou
Genhou 2014-1-24
Yes.I want to distribute into rectangular grid.
The data and the rectangular grid that I show are an examples to merely explain my question. Your suggestion is great. I would choose this way:(-35=<x<-30,-5=<y< 0),(-30=<x<-25,-5=<y=< 0),....(-5=<x<0,-5<y=<0).
Then How to get the distribution into rectangular grid?

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Walter Roberson
Walter Roberson 2014-1-24
mingrid = -30;
gridgap = 5;
xgrididx = 1 + floor((x - mingrid) ./ gridgap);
ygrididx = 1 + floor((y - mingrid) ./ gridgap);
gridcounts = accumarray( [xgrididx(:), ygrididx(:)], 1 );
Now gridcounts is an array of counts.
row K is the range (K - 1) * gridgap + mingrid <= x < K * gridgap + mingrid . Same calculation for column number and y.

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