Convert matrix into CSV, with each matrix element as a separate line including indices of matrix element

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Daniel 2022 年 9 月 17 日
コメント済み: Star Strider 2022 年 9 月 18 日
Struggling with writematrix and having to resort to odd things like appending repeating vectors to achieve this... I am sure there must be an easier way. The size of the matrix is such that for loops etc are terribly slow.
I have a matrix like this:
0.5 0.1 0.6
0.9 0.8 0.3
I'd like to output this as a CSV in the format x, y, e - where x and y are the column and row numbers and e is the element, to give something like this:
1, 1, 0.5
2, 1, 0.1
3, 1, 0.6
1, 2, 0.9
2, 2, 0.8
3, 2, 0.3

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採用された回答

Star Strider 2022 年 9 月 17 日
Try something like this —
M = [0.5 0.1 0.6
0.9 0.8 0.3];
[r,c] = ndgrid(1:size(M,1), 1:size(M,2));
rv = reshape(r.',[],1);
cv = reshape(c.',[],1);
Mv = reshape(M.',[],1);
A = [cv rv, Mv]
A = 6×3
1.0000 1.0000 0.5000 2.0000 1.0000 0.1000 3.0000 1.0000 0.6000 1.0000 2.0000 0.9000 2.0000 2.0000 0.8000 3.0000 2.0000 0.3000
Then use the writematrix function with a .csv suffix on the file name.
.
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Star Strider 2022 年 9 月 18 日
As always, my pleasure!

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その他の回答 (3 件)

Stephen23 2022 年 9 月 17 日

M = [0.5,0.1,0.6;0.9,0.8,0.3]
M = 2×3
0.5000 0.1000 0.6000 0.9000 0.8000 0.3000
N = M.';
S = size(N);
[X,Y] = ndgrid(1:S(1),1:S(2));
writematrix([X(:),Y(:),N(:)],'test.txt')
Checking:
type test.txt
1,1,0.5 2,1,0.1 3,1,0.6 1,2,0.9 2,2,0.8 3,2,0.3
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Stephen23 2022 年 9 月 17 日

@Dyuman Joshi: thanks, fixed now. That neatens things up too.

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Walter Roberson 2022 年 9 月 17 日
There are two possibilities here.
If you need every location output because in practice the data will be read as a vector of numbers and reshaped under the assumption that it is complete and in standard order, then use techniques like what Star Strider showed.
But if the individual coordinates are actively used then
[r, c, s] = find(YourMatrix);
writematrix([r, c, s], filename);
this will not write any zeros.
You would recover the matrix by reading as the columns as variables and passing them to sparse()
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Dyuman Joshi 2022 年 9 月 17 日
You can try this -
y=[0.5 0.1 0.6;0.9 0.8 0.3];
z=y';
mat=[repmat(1:size(y,2),1,size(y,1))' repelem(1:size(y,1),1,size(y,2))' z(:)]
mat = 6×3
1.0000 1.0000 0.5000 2.0000 1.0000 0.1000 3.0000 1.0000 0.6000 1.0000 2.0000 0.9000 2.0000 2.0000 0.8000 3.0000 2.0000 0.3000
And use writematrix() as Star Strider mentioned.

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