get fieldname of a data struct matlab

Question

I have the following nested struct:

hole 1x200 struct, diam 1x12 struct, which has the following fields: pos, freq1, fre12

That is:

hole(1 to 200).diam(1 to 12).pos
                            .freq1
                            .freq2

From a value (freq1 and freq2), I would like to obtain the field name of the struct. So I will need to find the value that matches with freq1 and freq2 and show the fieldname.

I tried to use structfun in order to apply a function to each field.

[struct.field]=structfun(@(x) find(x.freq1==27.059783995484867 & freq2==76.468355874897000))

But I guess I am writing something wrong on the code.

Also I create an anonymous fuction but I have the following error:

'Error using structfun / Inputs to STRUCTFUN must be scalar structures'

. How ever when I verified if an specific value of the struct is scalar, I have a positive answerd: isscalar(hole(130).diam(10))

I belive I more near the solution using this script:

myfun=@(yourarray,desiredvalue) yourarray==desiredvalue;
%//Apply function to each field of scalar structure, it SCALAR??
desiredfieldindex=myfun(structfun(@(x) x,hole),26.697046257785030) 
desiredFieldName=fNames(desiredFieldIndex)

I don´t know if I am in the rigth path, or I should utilize the function find. ALso I that case I don´t know how to implement it.

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

Couple of things.

FLOATING POINT VALUES! Careful!! Never compare a floating point value as val==0.3! do abs(val-0.3)<10^-8 or something similar. Read more here.
You are using structfun wrong. The function needs 2 arguments, and you are just passing 1! However, structfun will apply a function to each field so you are not using it rigth either in that sense. Lets see an example

example:

a.hithere=5;
a.notthis=3;
fun=@(x)x==5;
[isfive]=structfun(fun,a)


isfive =

     1
     0

As you can see, it applies the function to each of them. If you try to change the function to fun=@(x)x.hithere==5 you will get an error! As the function is applied to each field, and x.hithere.hithere or x.notthis.hithere do not exist.

If you want to check both values, you will need to check them independently making two separated calls to structfun or avoiding structfun and just making a for loop.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Sep 21, 2015 at 9:36

Ander Biguri

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8 Comments

Nicolas T. Over a year ago

I have been trying some examples, and when I implement your logic into my programs, it doesn´t work. My situation is the following

Ander Biguri Over a year ago

@NicolasT. "it doesnt work"? Why it doesn't work? because for the question asked, works.

Nicolas T. Over a year ago

I apologized @Ander, I was wrinting and I submit the comment, by mistake. My example is the following: hole(1).diam(1).pos=1; hole(1).diam(1).freq1=3;hole(1).diam(1).freq2=2; hole(2).diam(1).pos=2;hole(2).diam(1).freq1=4;hole(2).diam(1).freq2=5;y=struct2table(hole) %I would like to obtain the field from a freq1. In other words, find the field that has the same freq1. %For instance: freq1=3 %y=strcutfun(find(...)...); y=hole(1).diam(1) I would like to obtain this as the answerd I am new here, I don´t know how to edit well the comment

Ander Biguri Over a year ago

@NicolasT. I migth not have been clear enough, structfun does not allow you to insert an structure with multiple repeated fields, as .diam(1);.diam(2). You will need to loop.

Nicolas T. Over a year ago

Yes, not only am I able to create it, but also I can acces the data. hole(1).diam(1).freq1=3; hole(1).diam(2).freq1=2; hole(2).diam(1).freq1=7; hole(2).diam(2).freq1=9; I would like to find any frequency and obtain its field. For instance: find(freq1==9) Result: hole(2).diam(2). I hope I could clarify the situation

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