Create Structure from cell array with dot separation in string

Question

Philipp Pasolli 2022-6-30

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回答： Steven Lord 2022-6-30

Hi everyone,

I am reading in data from a measurements where the signal names are imported as a 1-dimensional cell array. The respective strings in the cell array represent the signal name. The signal names have been given already an inherent "structure" themselves.

What i want to do now is to automatically create a structure in matlab based on the signal names and then associate the respective measurements which per signal are a 1-dimensional numeric array.

To clarify and give an example, two strings would be for example:

{'em1500.eta_t.x []'   }
{'em1500.eta_t.y []'   }

I now want to automatically create a structure like:

measurements.em1500.eta_t.x = (The measurements taken);
measurements.em1500.eta_t.y = (The measurements taken);

Does anybody has an idea how to automate that process?

Best regards

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Stephen23 2022-6-30

编辑：Stephen23 2022-6-30

"Does anybody has an idea how to automate that process?"

Creation of invalid fieldnames cannot be "automated".

However rather than writing fragile/buggy code that forces meta-data into fieldnames, why not just simply store that meta-data as data in its own right? Then your code will be simpler, more robust, and much more efficient.

Philipp Pasolli 2022-6-30

Maybe my intention was not quite clear enough, if that is the case sorry.

measurements.em1500.eta_t.x = (The measurements taken);

In the scenario above, measurements would be the variable name of the structure. Then em1500 would be a fieldname of measurements, eta_t would be a fieldname within em1500 and x would be a fieldname within eta_t. Meaning that the structure ends up having three layers in that case if i am not wrong?

Since there is a lot of data from different "parts", to group the respective measurements in a logical ordere would make a lot of sense in my opinion, which is why i try to accomplish this in the first place.

Hope that explanation helped?

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Answer 1

Stephen23 2022-6-30

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编辑：Stephen23 2022-6-30

You can use SETFIELD() with a comma-separated list:

V = pi;
T = 'em1500.eta_t.x';
C = split(T,'.');
S = struct();
S = struct with no fields.
S = setfield(S,C{:},V)
S = struct with fields:
    em1500: [1×1 struct]

Checking:

S.em1500.eta_t.x
ans = 3.1416

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/1656435-tutorial-comma-separated-lists-and-how-to-use-them

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Answer 2

Fangjun Jiang 2022-6-30

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编辑：Fangjun Jiang 2022-6-30

If your question comes down to whether "em1500.eta_t.x" can be made a field name, then the anser is No. It is an invalid field name, just as you can't make "123 xyz" a variable name.

If you can make that name to be "em1500_eta_t_x", then you can use

MyStuct=struct('em1500_eta_t_x',rand)
MyStuct = struct with fields:
    em1500_eta_t_x: 0.1513

To establish a multi-layer structure, you can do it directly

clear a
a=struct
a = struct with no fields.
a.b.c.d=1
a = struct with fields:
    b: [1×1 struct]
a.b.c.d
ans = 1

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Philipp Pasolli 2022-6-30

编辑：Philipp Pasolli 2022-6-30

Thanks for the reply, but i dont think that is what i am looking for. I might have been not clear in my description.

See:Comment above

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Answer 3

Steven Lord 2022-6-30

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s = 'em1500.eta_t.x';
f = split(s, '.')
f = 3×1 cell array
    {'em1500'}
    {'eta_t' }
    {'x'     }

At this point you may want to use matlab.lang.makeValidName to ensure the field names (the 'pieces' of s) are valid identifiers.

mydata = setfield(struct, f{:}, 1)
mydata = struct with fields:
    em1500: [1×1 struct]
mydata.em1500
ans = struct with fields:
    eta_t: [1×1 struct]
mydata.em1500.eta_t
ans = struct with fields:
    x: 1

Alternately you might want to make this a table array with s as either the row name or (if you're using a release that supports table variable names that aren't valid identifiers) the variable name.

t1 = table(1, 'VariableNames', {s})
t1 = table
    em1500.eta_t.x
    ______________

          1       
y = t1.("em1500.eta_t.x")
y = 1
t2 = table(1, 'RowNames', {s})
t2 = table
                      Var1
                      ____

    em1500.eta_t.x     1  
z = t2{"em1500.eta_t.x", 1}
z = 1