How can I merge the values of one matrix into another matrix based on one column value?

Question

Mario 2022-9-22

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https://ww2.mathworks.cn/matlabcentral/answers/1809970-how-can-i-merge-the-values-of-one-matrix-into-another-matrix-based-on-one-column-value

评论： Chunru 2022-9-22

I have the following matrices:

A = zeros([7 4])
A(:,1) = 1104849000:60:1104849400
B = rand([3 4])
B(1,1) = 1104849000
B(2,1) = 1104849180
B(3,1) = 1104849240

And I would like to fill in the rows in matrix A with the values in matrix B based on the first column matching.

So the end result will be:

C = zeros([7 4])
C(:,1) = 1104849000:60:1104849400
C(1,:) = B(1,:)
C(4,:) = B(2,:)
C(5,:) = B(3,:)

Which would be the idiomatic way to achive this in Matlab (obviously for much larger matrices)?

Assumptions:

Matrix A will ALWAYS contain the values of the first column in Matrix B (so Matrix B is always a subset of Matrix A in terms of first column values).
Both Matrix A and B contain always sorted and unique values for the first column.

This is a simplified reproducible example, in my real example I am trying to ensure that an incomplete time series (Matrix B) fills a complete time series (Matrix A). First column are epoch seconds; in case there is another approach suitable for this.

Note: I want to learn how to use matrices, not TimeTables.

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Answer 1

Chunru 2022-9-22

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1809970-how-can-i-merge-the-values-of-one-matrix-into-another-matrix-based-on-one-column-value#answer_1058575

A = zeros([7 4]);
A(:,1) = 1104849000:60:1104849400;
B = rand([3 4]);
B(1,1) = 1104849000;
B(2,1) = 1104849180;
B(3,1) = 1104849240;
A, B
A = 7×4
1.0e+09 *

    1.1048         0         0         0
    1.1048         0         0         0
    1.1048         0         0         0
    1.1048         0         0         0
    1.1048         0         0         0
    1.1048         0         0         0
    1.1048         0         0         0
B = 3×4
1.0e+09 *

    1.1048    0.0000    0.0000    0.0000
    1.1048    0.0000    0.0000    0.0000
    1.1048    0.0000    0.0000    0.0000
C = zeros([7 4]);
C(:,1) = A(:, 1);
for i=1:height(C)
    idx = find(B(:,1) ==C(i,1), 1);
    if ~isempty(idx)
        C(i, :) = B(idx, :);
    end
end
C
C = 7×4
1.0e+09 *

    1.1048    0.0000    0.0000    0.0000
    1.1048         0         0         0
    1.1048         0         0         0
    1.1048    0.0000    0.0000    0.0000
    1.1048    0.0000    0.0000    0.0000
    1.1048         0         0         0
    1.1048         0         0         0

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Answer 2

Mario 2022-9-22

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https://ww2.mathworks.cn/matlabcentral/answers/1809970-how-can-i-merge-the-values-of-one-matrix-into-another-matrix-based-on-one-column-value#answer_1058600

编辑：Mario 2022-9-22

Additional to the answer above, I found that ismember can be also used here

A = zeros([7 4]);
A(:,1) = 1104849000:60:1104849400;
B = rand([3 4]);
B(1,1) = 1104849000;
B(2,1) = 1104849180;
B(3,1) = 1104849240;
format long
C=A
C = 7×4
1.0e+09 *

   1.104849000000000                   0                   0                   0
   1.104849060000000                   0                   0                   0
   1.104849120000000                   0                   0                   0
   1.104849180000000                   0                   0                   0
   1.104849240000000                   0                   0                   0
   1.104849300000000                   0                   0                   0
   1.104849360000000                   0                   0                   0
C(ismember(A(:,1),B(:,1)),:)=B(:,:)
C = 7×4
1.0e+09 *

   1.104849000000000   0.000000000797805   0.000000000828391   0.000000000912236
   1.104849060000000                   0                   0                   0
   1.104849120000000                   0                   0                   0
   1.104849180000000   0.000000000016681   0.000000000523010   0.000000000855862
   1.104849240000000   0.000000000730961   0.000000000517466   0.000000000437620
   1.104849300000000                   0                   0                   0
   1.104849360000000                   0                   0                   0