MATLAB: How to count the number of elements of a given value in a matrix

countlatitudelongitudematrix

I have a matrix such as.
44.147231 ; 24.358619
44.461415 ; 24.118248
44.258173 ; 23.185014
43.166729 ; 24.100443
43.159002 ; 26.708013
42.954059 ; 27.338612
44.139759 ; 23.927882
44.424679 ; 25.301393
42.957588 ; 25.530434
44.615223 ; 24.200719
44.384409 ; 25.486735
43.965701 ; 28.454219
43.400971 ; 21.492123
42.068687 ; 22.303336
43.245372 ; 28.932286
44.593751 ; 23.635179
The first column is longitude , the second column is latitude.
So, I want to count the number of region.
In the above matrix,
But I don't know how make the code.
Please help me…

Best Answer

Note: when posting examples, it' s much easier for us if you use proper matlab syntax. As it is, I had to paste your example in a text editor to remove the ; between the numbers.
As often the case in matlab, the most efficient solution is to avoid loops. The simplest way to solve your problem is to convert your latitude and longitude into matrix coordinates (by rounding down the numbers, subtracting the min of each column, and adding 1) and use these coordinates with accumarray to compute the histogram:
 %this can be pasted straight into matlab, your example can't:
 longlat = [44.147231   24.358619
            44.461415   24.118248
            44.258173   23.185014
            43.166729   24.100443
            43.159002   26.708013
            42.954059   27.338612
            44.139759   23.927882
            44.424679   25.301393
            42.957588   25.530434
            44.615223   24.200719
            44.384409   25.486735
            43.965701   28.454219
            43.400971   21.492123
            42.068687   22.303336
            43.245372   28.932286
            44.593751   23.635179]; 
gridcoord = floor(longlat); %get integer by rounding down
gridcoord = 1 + bsxfun(@minus, gridcoord, min(gridcoord)); %shift everything so offsets start at 1
gridpop = accumarray(gridcoord, 1)
gridpop is the population of each region. Note that longitude is the vertical coordinate, increasing down and latitude is the horizontal coordinate, increasing right. Like matrices in matlab. If you want it in the same format as in your example:
gridpop = flipud(gridpop')
Related Question