MATLAB Answers

## find matching values from two unequal size arrays

Asked by akk

### akk (view profile)

on 10 Nov 2018
Latest activity Commented on by akk

### akk (view profile)

on 11 Nov 2018
Accepted Answer by Stephen Cobeldick

### Stephen Cobeldick (view profile)

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.

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## 3 Answers

### Stephen Cobeldick (view profile)

Answer by Stephen Cobeldick

### Stephen Cobeldick (view profile)

on 10 Nov 2018
Edited by Stephen Cobeldick

### Stephen Cobeldick (view profile)

on 10 Nov 2018
Accepted Answer

>> 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

### akk (view profile)

on 11 Nov 2018
Thanks!

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### madhan ravi (view profile)

Answer by madhan ravi

### madhan ravi (view profile)

on 10 Nov 2018

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

akk

### akk (view profile)

on 10 Nov 2018
Thanks, but lon1 must also equal lon2
madhan ravi

### madhan ravi (view profile)

on 10 Nov 2018
[ia1,c1,ib1]=ismember(lon1,lon2)

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### Andrei Bobrov (view profile)

Answer by Andrei Bobrov

### Andrei Bobrov (view profile)

on 10 Nov 2018

Let:
a = [lat1 lon1 pCO2];
b = [lat2 lon2];
b(:,3) = a(ismember(a(:,1:2),b,'rows'),3);

akk

### akk (view profile)

on 10 Nov 2018
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?

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