How to get the projection of a 2D colorplot on x axis?

I have a 2D color plot as following:

how can I choose a region, for example 15 to 25 (axes not labelled in the figure.. the Y axis range from 0 to 40 in this figure) and project on X axis so that I get a 1D histogram? To make clear, the program should sum up the values along Y axis (from yrange 15 to 25) for each X values and then plot SumY against X. This will make a 1D projection of the colormap.

In order to plot the colormap (the above image), I am using the following code:

 A=load('Data.dat');
 Dat=[Data(:,1) Data(:,2)];
 nbins=[100 100]; 
 n=hist3(Dat,nbins);
 n1 = n;
 n1(size(n,1) + 1, size(n,2) + 1) = 0;
 xb = linspace(min(Dat(:,1)),max(Dat(:,1)),size(n,1)+1);
 yb = linspace(min(Dat(:,2)),max(Dat(:,2)),size(n,1)+1);
 figure
 pcolor(xb,yb,n1);

I tried the following:

 A1=[A(:,1) A(:,2)];
 index= find(A1(:,2)>=15&A1(:,2)<=25);
 New=A1(index,:);
 vp=sum(New,2);
 hist(vp,100)

But along the X axis in the histogram (hist(vp, 100)) it is showing the values from 15 to 65! but in real data (New in the code) it is from 0 to 40 only! something mistake in this code I think!

Thank you

Answer 1

[Image Analyst]

verticalProjection = sum(theArray, 2); % Sum horizontally along columns in each row.
horizontalProjection = sum(theArray, 1); % Sum vertically along rows in each column.