How to loop over a structure in matlab

Question

MattC 2023-2-27

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https://ww2.mathworks.cn/matlabcentral/answers/1920035-how-to-loop-over-a-structure-in-matlab

评论： Walter Roberson 2023-2-28

Hi, I am new to matlab and learning it. I have a 1(1X1) main struct which again has 5(1X1) nested structs inside it which has 3(1X100) tables and I would like to finally fetch the value of those 3 tables but not sure how. Please help

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MattC 2023-2-27

在 MATLAB Online 中打开

% I have this for loop I used to get to the table and it works as expected
% however if you see I am using Struct1{1} and Struct2{1} so this is only
% giving me the value of 1st elements I would like to reuse this same code
% and get values of all the elements not the 1st one. Is that possible?
for Struct1 = fieldnames(Data.Struct1)
    for Struct2 = fieldnames(Data.Struct1.(Struct1{1})) %Gets the value for Struct2
        for Table1 = fieldnames(Data.Struct1.(Struct1{1}).(Struct2{1})) %Gets the value for Table1
           Struct2_Table1 = (Data.Struct1.(Struct1{1}).(Struct2{1}));
        end
    end    
end

Stephen23 2023-2-27

编辑：Stephen23 2023-2-28

@Learn Matlab: Please upload some representative data in a MAT file by clicking the paperclip button. It does not have to be your top-secret data, just something with exactly the same arrangement. Data descriptions are rarely correct.

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Answer 1

Stephen23 2023-2-27

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https://ww2.mathworks.cn/matlabcentral/answers/1920035-how-to-loop-over-a-structure-in-matlab#answer_1181280

编辑：Stephen23 2023-2-27

在 MATLAB Online 中打开

As far as I can tell, this is your data structure (for simplicity I will define only two field Names, but the code works for any number of Names). I will assume that you really do mean table-type when you write the term "table":

S.Name1.Table1 = array2table(rand(7,5));
S.Name1.Table2 = array2table(rand(7,5));
S.Name1.Table3 = array2table(rand(7,5));
S.Name2.Table1 = array2table(rand(7,5));
S.Name2.Table2 = array2table(rand(7,5));
S.Name2.Table3 = array2table(rand(7,5));

I will assume that your goal is to vertically concatenate the tables together (even though I asked for clarification here, so far you have not specified this), and that you want them concatenated in the same order as the fields have. I will also assume that the tables have compatible sizes, types, column/variable names, etc.

C = struct2cell(S);
T = [C{:}]
T = 1×2 struct array with fields:
    Table1
    Table2
    Table3
T1 = vertcat(T.Table1)
T1 = 14×5 table
      Var1       Var2        Var3       Var4        Var5  
    ________    _______    ________    _______    ________

99227     0.4364     0.95854    0.33011     0.30881
12542      0.255      0.2363    0.20619     0.78108
011572    0.90123     0.88262     0.8375     0.91407
70267    0.46694    0.059236    0.67056     0.16106
69667    0.72092     0.64737    0.65369     0.78121
75244    0.63781     0.67781    0.63327     0.34179
026504    0.32164     0.20523    0.34102     0.57129
30376    0.66852     0.22986    0.69838    0.061212
49366    0.99997     0.23237    0.55552      0.9058
23795    0.11266     0.85971    0.51135     0.88532
14828    0.15646     0.53883    0.32337     0.96484
56345    0.87312     0.16723    0.32941      0.2775
3072    0.41575     0.59287    0.53829     0.61671
20481    0.28157     0.12718    0.59056     0.82286
T2 = vertcat(T.Table2)
T2 = 14×5 table
      Var1        Var2       Var3        Var4        Var5  
    ________    ________    _______    ________    ________

54563     0.38388    0.29637     0.37261     0.90489
037324     0.59359    0.53215     0.73093     0.38226
21604     0.33477     0.7297     0.55717     0.14877
17777      0.3707    0.56774     0.76761     0.62979
97126     0.79812    0.27897      0.6427     0.14614
87722     0.99473    0.57715     0.24911     0.74901
98824     0.42447    0.23163    0.052579    0.085909
90763     0.76468    0.21964    0.034569     0.16539
86225     0.20711    0.83592     0.14267     0.72307
073437     0.33883    0.35699     0.87312     0.24588
52598       0.554     0.7246      0.2518     0.85848
12421    0.019399    0.39709     0.61751    0.082109
33215     0.67097    0.20596     0.71881     0.29208
31202     0.20779     0.3271    0.063916     0.53378
T3 = vertcat(T.Table3)
T3 = 14×5 table
      Var1        Var2        Var3        Var4        Var5  
    ________    _________    _______    _________    _______

36188     0.096081    0.55646    0.0028935    0.47708
97371      0.66854    0.29259      0.77311     0.1254
51468    0.0064368    0.17519      0.88172    0.48252
035424      0.25941      0.639      0.95591    0.31873
55395      0.69916    0.50231       0.2845    0.39384
40546      0.96839     0.8114       0.4037    0.97745
6857      0.69703     0.7666      0.55353    0.92403
49166      0.46666    0.95838      0.59512     0.5872
16437      0.35974    0.70321     0.023214    0.17211
02512      0.62842    0.18175      0.19001    0.16561
12052      0.94594     0.4946      0.61787    0.55298
96801      0.69281    0.98424      0.52184    0.93673
57205      0.10585    0.62255      0.15836    0.62718
63864      0.42176    0.75274      0.19087    0.88685

This code uses comma-separated lists:

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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MattC 2023-2-27

Thanks for the quick response @Stephen23. I believe this works. However, a quick follow up question: Is there a way we would get the values for each Names as well. What I mean by that is right now we the variable T which has the Tables and then the T1 variable which has the table1 value for both names 1,2 and hence the 14x5.

So, when I say if there is a way we could get values for each names lets say we would have TN1 table with only Name1's data then another table TN2 with Name2's data separate?

Stephen23 2023-2-28

编辑：Stephen23 2023-2-28

在 MATLAB Online 中打开

"a way we could get values for each names lets say we would have TN1 table with only Name1's data then another table TN2 with Name2's data separate?"

Of course, just replace VERTCAT with a cell constructor:

C1 = {T.Table1}
C2 = {T.Table2}
C3 = {T.Table3}

Then you can access the data using basic, efficient indexing:

https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-cell-array.html

For example the 2nd Name of Table1:

C1{2}

Your request is confusing because earlier you wrote that you want "... to store those 3 final tables separately and not planning on giving them unique variable names... not planning on giving them unique variable names", i.e. that you expected exactly three output tables. Now you are apparently asking for exactly that which you stated you were not asking for. Changing what you request makes it harder to help you.

Do NOT force yourself into writing slow, complex, inefficient, buggy code by using dynamically-named variables:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

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Answer 2

Cameron 2023-2-27

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在 MATLAB Online 中打开

Depends on how your data is placed in the function. Like @Walter Roberson said, structfun works well if your data looks like this

T.S.X = rand(1,1000);
T.S.Y = rand(1,1000)*2;
T.S.Z = rand(1,1000)*3;
p = structfun(@median,T.S);
disp(p)

Another way to do it is to loop through them.

T.S.X{1} = rand(1,1000);
T.S.X{2} = rand(1,1000)*2;
T.S.X{3} = rand(1,1000)*3;
for xx = 1:length(T.S.X)
    disp(median(T.S.X{xx}))
end

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MattC 2023-2-27

在 MATLAB Online 中打开

So, the data I have looks something like:

(1x1 struct count (1) (parent struct)) - which again has (1x1 struct - count (5) (child struct)) - which finally has (1x100 tables count (3))

I am trying to build a for loop which can pass through both the parent and child struct variables and then get me to those 3 tables

Data Looks like:

MainData --> Name1 --> Table 1(1x100), Table 2(1x100), Table 3(1x100)

MainData --> Name2 --> Table 1(1x100), Table 2(1x100), Table 3(1x100)

MainData --> Name3 --> Table 1(1x100), Table 2(1x100), Table 3(1x100)

MainData --> Name4 --> Table 1(1x100), Table 2(1x100), Table 3(1x100)

MainData --> Name5 --> Table 1(1x100), Table 2(1x100), Table 3(1x100)

The reason behind building this loop dynamically is Name field or the second structure might or might not have 5 count. It might stop at Name3 or Name2. However, that is for sure that each name will have 3 tables. So, in my code below I could achieve getting the first name1 and its corresponding table 1 but I would like to fetch first how many names it has 1,2,3..5 and then fetch all the 3 tables

for Struct1 = fieldnames(Data.Struct1)
    for Struct2 = fieldnames(Data.Struct1.(Struct1{1})) %Gets the value for Struct2
        for Table1 = fieldnames(Data.Struct1.(Struct1{1}).(Struct2{1})) %Gets the value for Table1
           Struct2_Table1 = (Data.Struct1.(Struct1{1}).(Struct2{1}));
        end
    end    
end

Hope this information helps

MattC 2023-2-27

编辑：MattC 2023-2-27

@Stephen23, sorry I am really not at the liberty to share the data. I tried to be as elaborate as possible with the description sorry for the confusion it may have caused. So, I would like to store those 3 final tables separately and not planning on giving them unique variable names. I would just like store them as tables

Walter Roberson 2023-2-28

在 MATLAB Online 中打开

MainData --> Name1 --> Table 1(1x100), Table 2(1x100), Table 3(1x100)

Okay, that is 3 tables. Suppose you store those into variables named Table1, Table2 and Table3

MainData --> Name2 --> Table 1(1x100), Table 2(1x100), Table 3(1x100)

okay, that is 3 more tables. Do you want to now overwrite variables named Table1, Table2 and Table3 or do you want them stored into a different variable name?

If you were wanting to store to Table1{1} for Name1 and Table1{2} for Name2 and so on, using a cell array with one entry per field, then that is relatively easy. But if you want to store into (for example) Name1_Table1 and Name2_Table1 and so on, with the variable name depending on the field name, then the code gets uglier.

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