Splitting a matrix based on certain values in the rows
显示 更早的评论
I have a matrix A like this:
A = [911 911;
0 2;
8 5;
7 3;
911 911;
5 3;
1 6;
6 7;
911 911;
3 5;
8 4];
I want to split the matrix A into three matrices (A1,A2,A3) based on the row values 911 like this:
A1 = [0 2; 8 5; 7 3];
A2 = [5 3; 1 6; 6 7];
A3 = [3 5; 8 4];
I need to do this thing inside a for loop which will give the spitted matrix one after another.
3 个评论
Using numbered variables is a sign that you are doing something wrong.
Accessing variable names dynamically is one way that beginners force themselves into writing slow, complex, obfuscated buggy code that is hard to debug. Read this to know why:
You should use indexing instead. Indexing is simple, neat, and very efficient.
Mr. 206
2019-2-19
Jan
2019-2-19
@Atta: A,B,C, ... suffers from exactly the same problems as A1, A2, A3, ... With using a cell array and and index, the code is fast and flexibel. You can e.g. simply run it for 12'781'986 rows without getting mad while typing the code with manually hidden names of variables.
采纳的回答
No loop required:
>> idx = cumsum(all(A==911,2));
>> row = 1:numel(idx);
>> fun = @(r){A(r(2:end),:)};
>> C = accumarray(idx,row(:),[],fun);
>> C{:}
ans =
0 2
8 5
7 3
ans =
5 3
1 6
6 7
ans =
3 5
8 4
4 个评论
Mr. 206
2019-2-19
Stephen23
2019-2-19
"But i need a loop..."
Why?
"... and the resulted A1, A2 and A3 should be matrices."
They already are. Here is the first matrix:
>> C{1}
ans =
0 2
8 5
7 3
>> ismatrix(C{1})
ans = 1
>> isnumeric(C{1})
ans = 1
Jos (10584)
2019-2-20
% Pad each cell with rows of 911,
% so that it has the same number of rows as D
% using CELLFUN with an anonymous padding function using REPMAT
C2 = cellfun(@(m) [m ; repmat(911, size(D,1)-size(m,1),size(m,2))], C)
更多回答（1 个）
A = [911 911;
0 2;
8 5;
7 3;
911 911;
5 3;
1 6;
6 7;
911 911;
3 5;
8 4];
index = [find(A(:, 1) == 911); size(A, 1) + 1];
n = numel(index) - 1;
Result = cell(1, n);
for k = 1:n
Result{k} = A(index(k):index(k+1)-1, :); % [EDITED]
end
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