# How to conditionally pick the rows of tow datasets?

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Andi on 20 Jul 2022
Commented: Andi on 21 Jul 2022
Hi everyone,
I have two data set and want to pick rows that have common first element. In the below example, when first element of matrix A (row) is same with the first element of matrix B (row) the second element of B added to matrix A.
Thank you!
A = [1, 6, 3;
8, 11, 1;
4, 2, 0;
9, 2, 1]
B = [3, 11;
3, 1;
8, 4;
2, 5;
1, 8;
9, 7;
4, 6;
0, 1;
11, 25;
6, 15]
%% Dimesnions of A and B are not same
% then C
C = [1, 6, 3, 8;
8, 11, 1, 4;
4, 2, 0, 6;
9, 2, 1, 7]
% D be another empty arry that store the upper and lower values of second
% coloumn (B)
D=[4, 5, 8, 7, 6;
11, 1, 4, 5, 8;
8, 7, 6, 1, 25;
5, 8, 7, 6, 1]
% need to repeat this process for 5000 rows of column A, where the length
% of B is 17000
Here is the proposed methods alongwith the real data set, but none of them working on real data.
% Approach 1
B = array2table(B)
[ism,idx] = ismember(A(:,1),B(:,1));
C(ism,end+1) = B(idx(ism),2)
% Approach 2
C = outerjoin(A,B,'Key','Var1','Type','left')
The data is also attached here.

Voss on 20 Jul 2022
A = [1, 6, 3; 8, 11, 1; 4, 2, 0; 8, 1, 5; 9, 2, 1]
A = 5×3
1 6 3 8 11 1 4 2 0 8 1 5 9 2 1
B = [8, 4; 7, 1; 2, 5; 1, 8; 9, 7; 4, 6]
B = 6×2
8 4 7 1 2 5 1 8 9 7 4 6
C = A;
[ism,idx] = ismember(A(:,1),B(:,1));
C(ism,end+1) = B(idx(ism),2)
C = 5×4
1 6 3 8 8 11 1 4 4 2 0 6 8 1 5 4 9 2 1 7
Andi on 21 Jul 2022
Thanks, I already fixed that issue.

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