MATLAB: How to obtain values from a table in matlab

extract data from table in matlab

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?

Best Answer

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.

Related Solutions

MATLAB: How to extract specific values from a table

If I understand your question correctly, you want to measure the distance each (x,y) coordinate travels between frames. Is that correct? It looks like the (x,y) centers of your circles do not change between frames. For example, the first (x,y) coordinate at frame 1 is (144.09, 131,56) and this coordinate is the same for frame 2, 3, etc... When I run the code below, the distance is always 0. Maybe I'm not understanding your problem.

%% Import data and store in table "T"
opts = spreadsheetImportOptions("NumVariables", 4);
opts.Sheet = "in";
opts.DataRange = "A2:D30001";
opts.VariableNames = ["centreX", "centreY", "Radius", "Frame"];
opts.SelectedVariableNames = ["centreX", "centreY", "Radius", "Frame"];
opts.VariableTypes = ["double", "double", "double", "double"];
T = readtable("C:\Users\adanz\Documents\MATLAB\savehere\matlabCentralDocs_trash\DataTable_SER.xlsx", opts, "UseExcel", false);
%% Calculate distance between frames
nFrames = max(T.Frame); 
distFcn = @(x1,x2,y1,y2)sqrt((x2-x1).^2 + (y2-y1).^2);  %distance function
dist = nan(sum(T.Frame == 1), nFrames-1); %assumes there are an equal number of frames for all frames
for i = 2:nFrames
    % Index for frame i
    idx2 = T.Frame == i; 
    % Index for frame i-1
    idx1 = T.Frame == i-1; 
    % Calculate distance
    dist(:,i-1) = distFcn(T.centreX(idx2),T.centreX(idx1),T.centreY(idx2),T.centreY(idx1)); 
end

MATLAB: How to find the distances between two points in X-Y plane

Use euclidean distance

d = sqrt( (x2-x1).^2 + (y2-y1).^2 );

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MATLAB: How to extract specific values from a table

MATLAB: How to find the distances between two points in X-Y plane

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