How to add specific rows to a matrix?

9 次查看（过去 30 天）
Rodrigues Bitha
Rodrigues Bitha 2022-2-19
评论： Rodrigues Bitha 2022-2-19
I have a matrix A with 3 columns and multiple rows,
A =
a_1 b_1 2
a_1 b_1 3
a_1 b_1 2
a_2 b_2 6
a_2 b_2 8
a_3 b_3 3
a_3 b_3 9
a_3 b_3 5
a_3 b_3 4
... ... ...
For each couple of parameters (a_i, b_i) in A that appears less four times, I woud like to create a matrix B that contains additional rows "a_i b_i 0" for this couple of parameters, such that
B =
a_1 b_1 2
a_1 b_1 3
a_1 b_1 2
a_1 b_1 0 %added rows
a_2 b_2 6
a_2 b_2 8
a_2 b_2 0 %added rows
a_2 b_2 0 %added rows
a_3 b_3 3
a_3 b_3 9
a_3 b_3 5
a_3 b_3 4
... ... ...
Note that the value a_i and b_i ae not unique, but each couple (a_i, b_i) would be different from (a_j, b_j).
Thanks in advance!
  2 个评论
Image Analyst
Image Analyst 2022-2-19
Can you give an actual matrix with values?
TUTORIAL: How to ask a question (on Answers) and get a fast answer
I'm thinking that using findgroups() to find groups in the left column would be a part of the solution. If the length of any group is less than 4 you'd have to insert row(s).
Rodrigues Bitha
Rodrigues Bitha 2022-2-19
Here is an example of the matrix A
A =
3.8 6.4 2.0
3.8 6.4 5.0
3.8 6.4 9.0
3.8 6.5 4.0
3.8 6.5 3.0
3.9 6.4 1.0
3.9 6.4 8.0
3.9 6.4 7.0
3.9 6.4 4.0
And I would like to have this matrix B as a final result
A =
3.8 6.4 2.0
3.8 6.4 5.0
3.8 6.4 9.0
3.8 6.4 0.0 % added rows
3.8 6.5 4.0
3.8 6.5 3.0
3.8 6.5 0.0 % added rows
3.8 6.5 0.0 % added rows
3.9 6.4 1.0
3.9 6.4 8.0
3.9 6.4 7.0
3.9 6.4 4.0

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Voss
Voss 2022-2-19
Ran in:
A =[
3.8 6.4 2.0
3.8 6.4 5.0
3.8 6.4 9.0
3.8 6.5 4.0
3.8 6.5 3.0
3.9 6.4 1.0
3.9 6.4 8.0
3.9 6.4 7.0
3.9 6.4 4.0
];
needed_rows = 4;
[uA,~,jj] = unique(A(:,[1 2]),'rows','stable');
n_uA = size(uA,1);
B = [repelem(uA,needed_rows,1) zeros(needed_rows*n_uA,1)];
for ii = 1:n_uA
idx = jj == ii;
B(needed_rows*(ii-1)+(1:nnz(idx)),3) = A(idx,3);
end
disp(B);
3.8000 6.4000 2.0000 3.8000 6.4000 5.0000 3.8000 6.4000 9.0000 3.8000 6.4000 0 3.8000 6.5000 4.0000 3.8000 6.5000 3.0000 3.8000 6.5000 0 3.8000 6.5000 0 3.9000 6.4000 1.0000 3.9000 6.4000 8.0000 3.9000 6.4000 7.0000 3.9000 6.4000 4.0000

更多回答（1 个）

Image Analyst
Image Analyst 2022-2-19
Ran in:
Not sure why you didn't try findgroups() like I suggested. Or maybe you have by now. You might have gotten something like this:
A =[
3.8 6.4 2.0
3.8 6.4 5.0
3.8 6.4 9.0
3.8 6.5 4.0
3.8 6.5 3.0
3.9 6.4 1.0
3.9 6.4 8.0
3.9 6.4 7.0
3.9 6.4 4.0
];
g = findgroups(A(:, 1))
g = 9×1
1 1 1 1 1 2 2 2 2
neededRows = 8;
for k = 1 : max(g)
theseRows = g == k;
numInThisGroup = sum(theseRows);
if numInThisGroup < neededRows
lastRow = find(theseRows, 1, 'last');
rowsToAdd = neededRows - numInThisGroup;
% Insert rows.
A = [A(1:lastRow,:); repmat(A(lastRow, :), [rowsToAdd, 1]); A(lastRow+1:end, :)];
% Need to update g now.
g = findgroups(A(:, 1));
end
end
A
A = 16×3
3.8000 6.4000 2.0000 3.8000 6.4000 5.0000 3.8000 6.4000 9.0000 3.8000 6.5000 4.0000 3.8000 6.5000 3.0000 3.8000 6.5000 3.0000 3.8000 6.5000 3.0000 3.8000 6.5000 3.0000 3.9000 6.4000 1.0000 3.9000 6.4000 8.0000

类别

在 Help Center 和 File Exchange 中查找有关 Matrix Indexing 的更多信息

标签

产品


版本

R2019b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by