How to scan through several structures in MATLAB?

Question

I have some structure arrays (like structure1, structure2, structure3,...) with similar field names. I want to scan through all the structures and return only those whose first field is 5 (Field1==5). I have this code so far,

for k=1:3
    s=sprintf('Structure%d',k)
    Structure=load(s)
    idx=cellfun(@(x) x==5, {Structure.Field1})
    out=Structure(idx)
    v{k}={Structure.Field1}
end

but it gives me this error:

Reference to non-existent field 'Field1'.

Can someone please point out whats wrong here?

Thanx

Autonomous · Accepted Answer · 2013-02-24 18:59:09Z

0

for k=1:3
    s=sprintf('Structure%d',k)
    Structure=load(s)
    eval(['newStructure(k)=Structure.' s]);
    idx(k)=cellfun(@(x) x==5, {newStructure(k).Field1})
end
%extract the structures from newStructure which have 1 in idx
out=newStructure(idx); %idx should be a logical array
for i=1:size(out,2)
    v(i)=out(i).Field1;
end

This should work perfectly.

edited Feb 24, 2013 at 18:59

answered Feb 24, 2013 at 9:08

Autonomous

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6 Comments

user2091834 Over a year ago

There is a 'Field1' in every structure. The problem seems to be that Structures are stored in the workspace as Structure.Structure1.Field1. It doesn't work if I write {Structure.Structure(k).Field1} in the cellfun. Is there a way around it?

Autonomous Over a year ago

Why not extract out the structure into different variable as: newStruct=Structure.Structure1 and then proceed?

user2091834 Over a year ago

It works if I do it manually for each structure (Structure.Structure1, Structure.Structure2, ...) but how can I do that dynamically in the same loop?

user2091834 Over a year ago

It seems simple enough to do, but I am still struggling with it (I am relatively new at this). I just want to scan through multiple structures with same fields and save the structures which meets my search criteria into a separate vector. Is it even possible?

user2091834 Over a year ago

Thanx a lot. This works like a charm and returns the correct idx values (in 0 and 1). But when it comes out of the loop to out=newStructure(idx), it gives an error: "Index exceeds matrix dimensions". I'm sure its just a small glitch, but what does it mean?

|

Shai · Accepted Answer · 2013-02-24 09:09:00Z

0

It appears as if some of your saved structures do not have 'Field1' as a field in them.
In that case, you might want to try something else.
First define a function (in m-file)

function res = iff( cond, true_case, false_case )
%
% conditional execution of two function handles
% 
% true_case and false_case are function handles expecting no inputs
%
if cond
   res = true_case();
else
   res = false_case();
end

Once you have this function you can use it in the cellfun

idx = cellfun( @(x) iff( isfield(x, 'Field1'), @() x.Field1 == 5, @() false), Structure );

answered Feb 24, 2013 at 9:09

Shai

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2 Comments

user2091834 Over a year ago

There is a 'Field1' in every structure. The problem seems to be that Structures are stored in the workspace as Structure.Structure1.Field1. It doesn't work if I write {Structure.Structure(k).Field1} in the cellfun. Is there a way around it?

user2091834 Over a year ago

It seems simple enough to do, but I am still struggling with it (I am relatively new at this). I just want to scan through multiple structures with same fields and save the structures which meets my search criteria into a separate vector. Is it even possible?

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