match structures by table

Question

roblocks 2016-5-24

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评论： Guillaume 2016-5-24

Dear All, suppose you have two structures, A and B, where

 A.a
 A.b
 A.c

and

 B.1
 B.2
 B.3

Furthermore you have a table, which matches A to B, for example

b
a
c

bsed on this information, I would like to compute stuff using A and B. Both structures have the same number of fiels (which can all be uniquley matched between A and B). I need something like:

 for all *table* rows i:
    % computation using A.i, B.i;
 end

Is there a good way to solve this in Matlab?

Thanks in advance!

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Answer 1

Stephen23 2016-5-24

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编辑：Stephen23 2016-5-24

在 MATLAB Online 中打开

You can do this easily using dynamic fieldnames to access the structures. I do not have a MATLAB version with tables, but this example using a cell array should get you started:

A.a = 1;
A.b = 2;
A.c = 3;
B.x = 4;
B.y = 5;
B.z = 6;
C = {'b','x';'a','y';'c','z'};
out = NaN(size(C,1),1);
for k = 1:size(C,1)
    af = C{k,1};
    bf = C{k,2};
    out(k) = A.(af) + B.(bf);
end

produces the correct result:

>> out
out =
   6
   6
   9

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roblocks 2016-5-24

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Dear Stephen, yes that works!

For anyone else who is looking for the same thing, here is the code using tables:

 clear
A.a = 1;
A.b = 2;
A.c = 3;
B.x = 4;
B.y = 5;
B.z = 6;
C = {'b','x';'a','y';'c','z'}
s1 = {'a', 'b', 'c'}'
s2 = {'x', 'y', 'z'}'
T = table(s1, s2)
out = NaN(size(T,1),1)
for k = 1:size(C,1)
    af = C{k,1};
    bf = C{k,2};
    out(k) = A.(af) + B.(bf);
end

Guillaume 2016-5-24

在 MATLAB Online 中打开

Or simply:

out = rowfun(@(af, bf) A.(af) + B.(bf), T, 'OutputFormat', 'uniform')

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Answer 2

Guillaume 2016-5-24

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在 MATLAB Online 中打开

Probably the simplest way is to create a function with two inputs, the two field names. Your function then perform the calculation you want using dynamic field names as per Stephen's answer. You use rowfun to iterate over the rows of the table and call your function:

%in its own file (or as an anonymous function)
function result = somefuncname(structA, structB, fieldA, fieldB)
   result = structA.(fieldA) + structB.(fieldB);
end
%if using an anonymous function for somefuncname, then you don't need the funwrapper
%pass A and B straight to the function
funwrapper = @(fieldA, fieldB) somefuncname(A, B, fieldA, fieldB);
result = rowfun(funwrapper, yourtable)