MATLAB: Is there a way to extract a set of values from a structured array

MATLABstructured array values

I have defined a structured array, meas, which is indexed by number of occurrences of a phenomena. Thus, for example, I have: meas(n).ti = 65.32; meas(n).Rt = 200; meas(n).Vt = 10; etc., etc. I want to define a vector of, for example, the times of occurrences (the "ti" values). The pseudo-code would look like: 'TI = meas(1:end).ti' I obviously could do this in a loop: for n=1:nocc; TI(n) = meas(n).ti; end; (where nocc is the # of occurrences.) Is there a way to do this without using a loop?

Best Answer

Use a comma separated list:

[meas.ti]

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Comma separated lists are really very simple. You use them all the time. Here is one:

 a,b,c,d

There is a comma separated list containing four variables, the variables a, b, c, and d. Every time you write a list of variables separated by commas then you are writing a comma separated list. Most commonly you would write a comma separated list when calling a function or operator:

 fun(a,b,c,d)

It is important to note that a comma separated list is not one variable! Sometimes we want to create a comma separated list from one variable: MATLAB has two ways of doing this, these are from a cell array:

 cell_array{idx}

and from a structure:

 ND_struct.field

But both of these are still exactly equivalent to what I wrote at the top: they will generate this:

 variable1,variable2,variable3,...

and remember NOT ONE VARIABLE. Therefore the syntax you used:

 A(:).B.C

is an error because

 A(:).B

creates a comma-separated list, exactly equivalent to this:

 A(1).B,A(2).B,A(3).B,...

and it is ambiguous what role the .C should have on the end.

Because this

 A(:).B

is exactly equivalent to writing this list of independent variables:

 A(1).B,A(2).B,A(3).B...

and yet would you expect to write this list of independent variables:

 X,Y,Z.C

and expect it to get the C field of X, Y, and Z?

MATLAB: Multi-dimensional array, minimum, coordinate

a=rand(3,4,5);
[min_v,idx]=min(a(:))
[ii,jj,kk]=ind2sub(size(a),idx)

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