I got error : Names of fields in structure arrays being concatenated do not match. Concatenation of structure arrays requires that these arrays have the same set of fields.

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sam CP 2017-3-23

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评论： Walter Roberson 2017-3-26

I have used the following files and the error is :

Error using vertcat Names of fields in structure arrays being concatenated do not match. Concatenation of structure arrays requires that these arrays have the same set of fields.

Error in linearsyntax (line 16) test=[test0;test1];

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sam CP 2017-3-23

Error using vertcat Names of fields in structure arrays being concatenated do not match. Concatenation of structure arrays requires that these arrays have the same set of fields.

Error in linearsyntax (line 16) test=[test0;test1];

Image Analyst 2017-3-24

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What does this show:

fieldnames(NormalMRI);
fieldnames(AbnormalMRI);

If they don't show the same fieldnames, which is what the error is saying, then exactly what are you trying to do?

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Answer 1

Walter Roberson 2017-3-23

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The return value from load() is a structure with one field for each variable stored in the mat file. Even without opening the mat files I can tell that your code instead expects the return value to be the content of a single variable stored in the mat file. You will need to refer to the appropriate field name of the returned structure.

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Walter Roberson 2017-3-26

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What is the intention of your lines

training0=NormalMRI(4:1,:);
training1=AbnormalMRI(4:1,:);
test0=NormalMRI(8:5,:);
test1=AbnormalMRI(8:5,:);

In MATLAB, when you have a ":" operator such as 4:1 in which the number before the ":" is larger than the number after the ":", then the result is the empty range.

If your intention is to select rows 1 to 4, you need 1:4 instead of 4:1:

training0=NormalMRI(1:4,:);
training1=AbnormalMRI(1:4,:);
test0=NormalMRI(5:8,:);
test1=AbnormalMRI(5:8,:);

If your intention is to select one row starting from row 4, then you would use

training0=NormalMRI(4:4+1-1,:);
training1=AbnormalMRI(4:4+1-1,:);
test0=NormalMRI(8:8+5-1,:);
test1=AbnormalMRI(8:8+5-1,:);

But then after that you construct group as length 20, in a way that suggests you wanted 10 entries from each in your "training" set. Since your total now of entries in each is 4, my guess is that what you are after is:

NormalMRI= load1('TrainNormalMRI.mat');
AbnormalMRI = load1('TrainAbnormalMRI.mat');
training0=NormalMRI(1:10,:);
training1=AbnormalMRI(1:10,:);
test0=NormalMRI(11:end,:);
test1=AbnormalMRI(11:end,:);
zero=zeros(10,1);
one=ones(10,1);
group=[zero;one];
test=[test0;test1];
training=[training0;training1];
classify(test,training,group)
[IDX,Z]=rankfeatures(training',group);

If you run this then you will get into classify okay, but it will tell you:

The pooled covariance matrix of TRAINING must be positive definite.

You have some work to do in order to correct that. Read https://www.mathworks.com/matlabcentral/newsreader/view_thread/156518

sam CP 2017-3-26

编辑：sam CP 2017-3-26

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 function r = load1(filename) 
     t = load(filename) ;
     f = fieldnames(t) ;
     r = t.(f{1});

The code works for my program..Can you explain that how this matlab code works?

Walter Roberson 2017-3-26

The return value from load() is a structure with one field for each variable stored in the mat file. This code does a load() and queries the field names of the resulting structure and picks the first one. It then does dynamic field name referencing to extract the content of the field.

The net result is to return the content of the "first" variable stored in the .mat file.

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