MATLAB Answers


Transformation of the Matrix in a Loop

Asked by Irfan Tahir on 7 Oct 2019
Latest activity Commented on by Irfan Tahir on 9 Oct 2019
Hello Everyone,
I have the measurement mapping field which looks has dimensions 100x100 as shown
Now i want to turn this mapping to a column matrix of 10000x 3 like shown in the figure
How would i be able to do it. I tried for loop but the result is only 100x3
my code is something like zhis
for i=1:109
your_result = [X,Y,D]
I want this loop to keep adding values but couldnt able to work it out. Any assistance would be highly appreciable.
Irfan Tahir


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2 Answers

Answer by Guillaume
on 7 Oct 2019
 Accepted Answer

With your invented notation it's difficult to know what you actually have in matlab.
Assuming you have a matrix such as:
Z = [NaN 1 1.5 2 2.5 3
1 0.2 0.3 0.4 0.5 0.6
1.2 0.3 0.9 1.2 1.5 1.8
1.6 0.4 1.2 1.6 2.0 2.4
1.8 0.5 1.5 2.0 2.5 3.0]
Obtaining your desired result is easy and no loop is needed:
[Y, X] = ndgrid(Z(2:end, 1), Z(1, 2:end));
D = reshape(cat(3, X, Y, Z(2:end, 2:end)), [], 3)

  1 Comment

yes, it worked, thanks alot. The software we uses is Uniplot and it doesnt plot like Matlab do. So needed the data in colum form.
Thanks alot

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Answer by Jon
on 7 Oct 2019

Sorry, I inadvertently deleted my earlier response.
So I'm assuming you want an array with
y1 x1 z11
y2 x2 z21
y3 x3 z31
y1 x2 z12
y2 x2 z22
This isn't the way you have it in your original question but maybe you just didn't type it correctly.
It could probably be vectorized (avoid a loop) but here is how you could do it with a loop
[numRows,numCols] = size(Z)
Ztbl = zeros(numRows*numCols,3)
row = 1
for j = 1:numCols
for i = 1:numRows
Ztbl(row,:) = [y(i) x(j) Z(i,j)]
row = row+1


on 7 Oct 2019
You can also vectorize it and avoid loops using
Ztbl = [repmat(y(:),numCols,1) repelem(x(:),numRows) Z(:)]
thanks for the help.

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