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How to obtain values from a table in matlab

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karishma koshy
karishma koshy on 14 Jul 2019
Edited: karishma koshy on 15 Jul 2019
I have a table with two columns as circle's centre position and third one with frame number 1-1000. I want to obtain the values of circle centres in frame n and n-1 at a time, inorder to make matrix out of it
How can I do that?

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Adam Danz
Adam Danz on 14 Jul 2019
Edited: Adam Danz on 14 Jul 2019
I'm not sure what you mean by "in order to make a matrix out of it". If this demo doesn't address the problem, please provide an example. Otherwise, here's how to extract the (x,y) coordinates for a given frame.
%Fake data
T = table((1:9)',(2:10)',[1;1;1;2;2;2;3;3;3],'VariableNames',{'X','Y','Frame'});
f = 2; % frame number
frameIdx = T.Frame == f; %row numbers of frame n
frameIdx = T.Frame == f-1; %row numbers of frame n-1 (not used in this demo)
% FROM HERE YOU CAN DO LOTS OF THINGS LIKE...
% ...isolate rows of table that belong to frame n
T(frameIdx,:)
% ...isolate only the (X,Y) values that belong to frame n
T(frameIdx,{'X','Y'})
% ...put (X,Y) values from frame n into a matrix
T{frameIdx,{'X','Y'}}
I recommend keeping the data in the table rather than extracting it into a matrix unless your analysis requres a matrix.

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karishma koshy
karishma koshy on 14 Jul 2019
Dear sir
Can you help me construct a for loop to find the distance between loops in n and n-1 frames and terminate the loop when it's reached the last value of both the frames
Adam Danz
Adam Danz on 15 Jul 2019
The loop will probably look something like this; T is your table.
% Create fake data
T = table((1:9)',(2:10)',[1;1;1;2;2;2;3;3;3],'VariableNames',{'X','Y','Frame'});
n = size(T,1)'; %number of rows in your table
distFcn = @(x1,x2,y1,y2)sqrt((x2-x1)^2 + (y2-y1)^2); %distance function
% Loop through each row starting at row #2
d = zeros(n-1,1); %create a vector where the distances will be stored
for i = 2:n
d(i-1) = distFcn(T.X(i-1),T.X(i),T.Y(i-1),T.Y(i));
end
And you can do that without a loop, too.
distFcn = @(x1,x2,y1,y2)sqrt((x2-x1).^2 + (y2-y1).^2); %distance function
% ^ ^ note the dots
d = distFcn(T.X(2:end),T.X(1:end-1),T.Y(2:end),T.Y(1:end-1))
karishma koshy
karishma koshy on 15 Jul 2019
Dear Sir I'm aiming to measure the distance between all points in one frame and all points in the next frame. So I want to
Create a table (let’s call this “table i”)which only contains points in frame i (where “i" is the index of that frame) Create another table (“table i+1”), which only contains points in frame i+1 Create a 2D distance matrix (width equal to the number of points in frame i and height equal to the number of points in frame i+1) where each element is the Pythagoras distance between two points.
How can I implement this as a code ? Thank you

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