Convert matrix into CSV, with each matrix element as a separate line including indices of matrix element
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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
Suggestions/advice/solutions greatly appreciated :)
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Accepted Answer
Star Strider
on 17 Sep 2022
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]
.
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More Answers (3)
Stephen23
on 17 Sep 2022
Edited: Stephen23
on 17 Sep 2022
M = [0.5,0.1,0.6;0.9,0.8,0.3]
N = M.';
S = size(N);
[X,Y] = ndgrid(1:S(1),1:S(2));
writematrix([X(:),Y(:),N(:)],'test.txt')
Checking:
type test.txt
2 Comments
Dyuman Joshi
on 17 Sep 2022
@Stephen23 the order of the output of main array is not correct. You need to transpose M before using the command M(:)
Stephen23
on 17 Sep 2022
Edited: Stephen23
on 17 Sep 2022
@Dyuman Joshi: thanks, fixed now. That neatens things up too.
Walter Roberson
on 17 Sep 2022
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
on 17 Sep 2022
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(:)]
And use writematrix() as Star Strider mentioned.
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