find matching values from two unequal size arrays

I have two arrays of unequal length. [lat1 lon1 pCO2] say 200000 values in each column [lat2 lon2] say 100000 values in each column

I want to find where both lat2=lat1 and lon2=lon1, then take the pCO2 value from the first array and plug it into the second array as a new column.

Answer 1

[Stephen23]

>> A1 = [1,2,3;4,5,6;7,8,9]
A1 =
     1     2     3
     4     5     6
     7     8     9
>> A2 = [1,2;0,0;0,0;4,5]
A2 =
     1     2
     0     0
     0     0
     4     5
>> [ida,idb] = ismember(A2,A1(:,1:2),'rows');
>> A2(:,3) = NaN;
>> A2(ida,3) = A1(idb(ida),3)
A2 =
     1     2     3
     0     0   NaN
     0     0   NaN
     4     5     6

[akk]

Thanks!

Answer 2

[madhan ravi]

[ia,c,ib]=ismember(lat1,lat2)

[akk]

Thanks, but lon1 must also equal lon2

[madhan ravi]

[ia1,c1,ib1]=ismember(lon1,lon2)

Answer 3

[Andrei Bobrov]

Let:

a = [lat1 lon1 pCO2]; 
b = [lat2 lon2];

b(:,3) = a(ismember(a(:,1:2),b,'rows'),3);

[akk]

Thanks! This works! Only, because there are some rows in b without a match in a, b (:,3) is smaller than the number of rows in b. Is there a way to fill in those missing rows with a nan instead?