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How to extract data from a multi layered structure

Asked by Bluegin on 22 Aug 2019 at 14:30
Latest activity Edited by Stephen Cobeldick on 23 Aug 2019 at 3:04
Hi,
I have a multi-layered structure A that include 3 structures (a, b and c) and and all of them contain 10 fieldnames with 10 rows and every cell further contains 10 double numbers mixed with nans.
Doing
A.b.fieldname1
yields the content of the first cell (10 double), but I cant seem to to be able to extract the entire fielname. Doing
c = cell2mat(struct2cell(A.b.fieldname1(1,1)))
yields the following error: Expected one output from a curly brace or dot indexing expression, but there were 10 results.
So how can I extract the data from this multi-layered structure ?
Thank you,

  6 Comments

"My reading of your question is that you have a scalar structure A with 3 fields, themselves scalar structures, each with 10 fields"
If that were the case, then the error message "Expected one output from a curly brace or dot indexing expression..." would not occur. One or more of the structures is non-scalar. As far as I can tell, the original explanation simply omits this important information.
"Lets say I had a structure like this..:"
But in your question you clearly describe nested structures.
With nested structures, you will have to use loops (implicitly or explicitly).
If you really had a structure "like this" (without nested structures), then you could simply use arrayfun or comma-separated list syntax to access your data, no loops required:
Without answering our questions or providing sample data, we have to rely on guessing. Guessing is not a reliable way for you to get help.
My apologies. My attempts at simplifying reality has caused more harm than good.
Lets start over. I have the structure attached here.
How can i calculate the minimum of a given field (min_temp for example) ? Thats why I want to extract the data.
Your structure is non-scalar:
>> load('PMAN_climatology.mat')
>> size(pman_climatology)
ans =
1 14
That explains the error message you give in your question.
Not only that, but none of its fields contain nested structures:
>> F = @(s)any(structfun(@isstruct,s));
>> arrayfun(F,pman_climatology)
ans =
0 0 0 0 0 0 0 0 0 0 0 0 0 0
"How can i calculate the minimum of a given field (min_temp for example)?"
You don't define "the minimum" for mutliple vectors: do you want the global minimum, or the minimum of each vector, or the minimum of each column when the vectors are concatenated into one matrix, or some other minimum?

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1 Answer

Answer by Stephen Cobeldick on 22 Aug 2019 at 16:38
Edited by Stephen Cobeldick on 23 Aug 2019 at 3:04

"How can i calculate the minimum of a given field (min_temp for example) ?"
You do not define what "the minimum" means for multiple vectors, which makes it hard to guesss what output you expect...
Method one: comma-separated list and cellfun:
For example:
>> vec = cellfun(@min,{pman_climatology.min_temp})
vec =
1.0000 4.6000 3.0000 3.0000 2.1000 2.5000 2.0000 2.0000 6.5000 1.5000 1.0000 1.5000 4.1000 1.0000
That gives the minimum value of the field min_temp for each element of the structure pman_climatology. Compare with the first few elements of pman_climatology:
>> min(pman_climatology(1).min_temp)
ans =
1
>> min(pman_climatology(2).min_temp)
ans =
4.6000
>> min(pman_climatology(3).min_temp)
ans =
3
Method two: anonymous function and arrayfun:
>> F = @(s)min(s.min_temp);
>> arrayfun(F,pman_climatology)

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