# How to define a struct array with length more than one and assign values to one of the strucy array?

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Benson Gou on 12 Oct 2020
Commented: Benson Gou on 12 Oct 2020
Dear All,
I have a real array A. I want to define a struct array S to save the colculation reslut of element in A to the corresponding struct.
For example, A = [1 0.2 3 0.4 5 6]. I want to define strucy array S (with length 6) to save the calaulation result of elements in A.
S(1) = struct('A.1', A(1), 'Result', A(1)^2);
S(3) = struct('A.3', A(3), 'Result', A(3)^2);
S(4) = struct('A.4', A(4), 'Result', A(4)^2);
S(6) = struct('A.6', A(6), 'Result', A(6)^2);
I only want to save these 4 values.
My question is:
1). How to define S?
2). How to assign values to S?
Thanks a lot.
Benson

Stephen Cobeldick on 12 Oct 2020
Edited: Stephen Cobeldick on 12 Oct 2020
>> A = [1,0.2,3,0.4,5,6];
>> X = [1,3,4,6]; % "I only want to save these four values"
>> Ac = num2cell(A);
>> Bc = num2cell(A.^2);
>> S = repmat(struct(),1,6);
>> [S(X).A] = Ac{X};
>> [S(X).B] = Bc{X};
>> S.A
ans = 1
ans = []
ans = 3
ans = 0.40000
ans = []
ans = 6
>> S.B
ans = 1
ans = []
ans = 9
ans = 0.16000
ans = []
ans = 36

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Stephen Cobeldick on 12 Oct 2020
>> A = [1,0.2,3,0.4,5,6];
>> X = [1,3,4,6];
>> C = {[3,1],-2,[5,10,23],[-7,2,11,38]};
>> S = repmat(struct(),1,6);
>> Ac = num2cell(A);
>> [S(X).A] = Ac{X};
>> [S(X).Values] = C{:};
>> S.A
ans = 1
ans = []
ans = 3
ans = 0.40000
ans = []
ans = 6
>> S.Values
ans = 3 1
ans = []
ans = -2
ans = 5 10 23
ans = []
ans = -7 2 11 38
Steven Lord on 12 Oct 2020
Are you required to store your data in a struct array, or would a cell array be acceptable?
c = cell(1, 10);
for k = 1:10
c{k} = magic(k);
end
celldisp(c)
Benson Gou on 12 Oct 2020
Thanks, Stephen, It works well.
Benson

Steven Lord on 12 Oct 2020
Edited: Steven Lord on 12 Oct 2020
A.1 is not a valid struct field name.
With something this simple, I probably wouldn't use a struct array.
A = [1 0.2 3 0.4 5 6]
Asquared = A.^2
If you wanted to store these in one array rather than two, since the result of the operation is the same type and size as the data on which you're operating, you can store them as rows of the array:
B = [A; Asquared]
or as a table array:
C = table(A.', Asquared.', 'VariableNames', ["A", "A^2"]) % If you're using R2019b or later
C = table(A.', Asquared.', 'VariableNames', ["A", "A_squared"]) % R2019a or earlier