# Modifying a structure array

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SS on 11 Aug 2019
Edited: Bruno Luong on 26 Aug 2019
Hi. I am working with a structure array, and I want to modify the structure based on a condition on the field entries.
For example,
Here is the input,
S(1).f1=[1:100] and S(2).f2=[2:101];
S(2).f1=[40:120] and S(2).f2=[60:140]
S(3).f1=...... and S(3).f2=.....
S(4).f1=.... and S(4).f2=.....
.
.
S(i).f1=.... and S(i).f2=....
Can anyone suggest me some smart way to do this.
Conditions on input Output
S(1).f1>=0 and S(1).f1<=50 then ------> S(1).f1=[1:50] and S(1).f2=[2:51]
S(1).f1>50 and S(1).f1<=100 then ------>S(2).f1=[51:100] and S(2).f2=[52:101]
.... so on
Now, the same process for original/input S(2).f1, S(3).f1 .... S(i).f1 to re-form the structure.
After, modification the final step is to delete S(i) if the size of S(i).f1 is < 5.

Rik on 11 Aug 2019
So when a split occurs the new entry should be put between the parent position and the position after it? Under that assumption I'll edit my answer.
And where are those condition values coming from?
Stephen Cobeldick on 11 Aug 2019
SS on 12 Aug 2019
Hi Rik. The order doesn't matter, I just want them them to form a new column. It is from some biological process and I have to break the structure for a span of 50 units of a given field.

Bruno Luong on 12 Aug 2019
Edited: Bruno Luong on 12 Aug 2019
S=struct;
S(1).f1=5*[2,3,4,5,6,7,8,10,14,16,18,20];
S(1).f2=5*[3,6,9,12,15,18,21,24,27,30,33,36];
S(2).f1=40:120;S(2).f2=60:140;
S(3).f1=20:100;S(3).f2=40:120;
b = arrayfun(filtfun, S, 'unif', 0);
Sfilter = arrayfun(@(s,b) structfun(@(a) a(b{1}), s, 'unif', 0), S, b); % your reasult
I let you do the deletion step.

SS on 26 Aug 2019
Hi. I am unable to upload the S.dat file because, of its large size. I am using the field "growth" to re-arrange my structure. Here are some entries to give an idea about the type of data.
S(1).growth=[69.0899,69.1163,69.1295,69.1212,69.0978,69.0671];
S(2).growth=[68.6689379657871 68.6012576662520 68.5432527036940 68.5183488830736 68.4623425084315 68.4032211916516 68.4089831038520 68.4303882075090 68.4787272982599 68.4441422394964 68.3360147869897 68.2795868644623];
S(3).growth=[40.6236,40.2163,39.8215,39.4620,39.1736,38.9691];
S(4).growth=[65.3854,64.8621,64.3253,63.7556,63.1388];
...... so on.
filtfun = @(s) s.growth>=0 & s.growth<=50;
b = arrayfun(filtfun, S, 'unif', 0);
Sfilter = arrayfun(@(s,b) structfun(@(a) a(b{1}), s, 'unif', 0), S, b);
Sfilter(cellfun(@sum,b)<5) = []
S1=Sfilter;
After clearing the above variables
filtfun = @(s) s.growth>50 & s.growth<=100;
b = arrayfun(filtfun, S, 'unif', 0);
Sfilter = arrayfun(@(s,b) structfun(@(a) a(b{1}), s, 'unif', 0), S, b);
Sfilter(cellfun(@sum,b)<5) = []
S2=Sfilter;
Rik on 26 Aug 2019
Neither code section produces the error you indicate. You should try to find a data line that causes this error. That is one of the hallmarks of an MWE: the smallest section of data and code that produces the error.
Often when trying to create an MWE you already find the mistake on your own. I have sometimes started writing my own question, when I found the mistake when creating an MWE for my post.
Bruno Luong on 26 Aug 2019
SS: "Hi again. I have tried to use the above code and unfortunately, it gives the follwoing error."
This error is expected to me because you wrote:
"For each S(i), the length of the field arrays is same throughout except 5 fields. The length of these 5 fields is 1 less than the other 25 field arrays. The last element in the these fields can be conisder as zero or empty, it doesn't matter."
Actually it does MATTER, contrary to what you wrote.
And I have warned you long ago.
"I let you deal with the exception of one less element on 5 fields (that's messy condition, and bad data structure design), you better fill them with trailing 0 or NaN, whatever suitable for you, to make all the fields have the same length."

Rik on 11 Aug 2019
Edited: Rik on 11 Aug 2019
Since you don't provide any indication of how you want this to work for struct array input, you'll have to modify this code yourself.
S=struct;
S(1).f1=[2,3,4,5,6,7,8,10,14,16,18,20];
S(1).f2=[3,6,9,12,15,18,21,24,27,30,33,36];
L=S(1).f1<=10;
if sum(L)>=5
S(2).f1=S(1).f1(L);
S(2).f2=S(1).f2(L);
end
S(1).f1(L)=[];S(1).f2(L)=[];
Edit:
%create input struct
S=struct;
S(1).f1=5*[2,3,4,5,6,7,8,10,14,16,18,20];
S(1).f2=5*[3,6,9,12,15,18,21,24,27,30,33,36];
S(2).f1=40:120;S(2).f2=60:140;
S(3).f1=20:100;S(3).f2=40:120;
%create the cell array that will hold the struct elements
c=cell(2,numel(S));
for n=1:numel(S)
c{1,n}=S(n);
L=S(n).f1<=50;
if sum(L)>=5
c{2,n}.f1=S(n).f1(L);
c{2,n}.f2=S(n).f2(L);
end
c{1,n}.f1(L)=[];c{1,n}.f2(L)=[];
end
%reshape back to a struct
S=[c{:}];

Show 1 older comment
Rik on 12 Aug 2019
That is not working because you use && instead of &. The single operator should be used for arrays, the double operator for scalars.
For numbered fields you could use a loop like this:
for n=1:5
S.(sprintf('f%d',n)) = rand;
end
SS on 12 Aug 2019
Thank you. What should be the approach if these are not numbered fields and some specific names?
Rik on 12 Aug 2019
The .() syntax works for char array inputs (and scalar strings).