Finding precipitation of specific coordinate matrix

Hi, I have a precipitation data that includes 3 columns. First column shows latitudes, second column shows longitudes and last one shows precipitation values. Suppose, I have A matrix:

A = 36  35  100
    36  34  78    
    36  33  42
    36  32  51
    35  35  83
    35  34  72
    35  33  80    

Here each columns show lat, lon and precipitation values of big region. But I want to extract precipitation values of specific B matrix that is shown below.

B= 36 33
   36 32
   35 33

so the precipitation values of that coordinates should be equal to R= 42, 51, 80. How can I wrote this code in matlab ? Thanks for your help.

Answer 1

[David Fletcher]

A = [36  35  100;
    36  34  78;    
    36  33  42;
    36  32  51;
    35  35  83;
    35  34  72;
    35  33  80 ; ]

index=(A(:,3)==42|A(:,3)==51|A(:,3)==80)

selction=A(index,1:2)

[Gokhan Kayan]

Thanks for the reply David but this is not what I exactly want. I dont want to find precipitation coordinates, I want to find precipitation values of B coordinate matrix. I have so many coordinates and ı want to extract precipitaion values of specific coordinates that is given by B matrix

[David Fletcher]

Sorry, misread it. Just switch the logic around a bit:

A = [36  35  100;
    36  34  78;    
    36  33  42;
    36  32  51;
    35  35  83;
    35  34  72;
    35  33  80 ; ]

index=(A(:,1)==36&A(:,2)==33)|(A(:,1)==36&A(:,2)==32)|(A(:,1)==35&A(:,2)==33)

selction=A(index,3)

[Gokhan Kayan]

Thats the way I want but the problem is my real B matrix is 600x2. It means ı have 600 lat and lon values. So I need to the write them 600 times using this script.

index=(A(:,1)==B(:,1)|A(:,2)==B(:,2));

I wrote this script but it says matrix dimension must agree.

[David Fletcher]

You wouldn't be using all rows of the B matrix, just a specific value for each check so B(1,1) rather than B(:,1) and so on... However, I'm not sure you really want to be writing an expression of that magnitude. Since B is so large a loop may be a better idea to build the indexing matrix by iterating through each row of B and checking it against A - Something like this:

A = [36  35  100;
    36  34  78;    
    36  33  42;
    36  32  51;
    35  35  83;
    35  34  72;
    35  33  80 ; ];

B= [36 33;
   36 32;
   35 33];

%Preallocate logical indexing vector to the number of rows in A. Set
%initial condition to no match (false)
positions=false(size(A,1),1);

for rowIndex=1:size(A,1)
    %Check each longitude and latitude position in B against each row of A
    for entries=1:size(B,1)
        if (A(rowIndex,1)==B(entries,1)&&A(rowIndex,2)==B(entries,2))
            %If position matches set indexing vector
            positions(rowIndex)=true;
        end
    end   
end

%Show rainfall for matching longitude and latitude entries
rainfall=A(positions,3)

[Gokhan Kayan]

Thanks dear David, It perfectly worked now.