You are right – sorry about that!

–loren

ufn = length(fn) == unique(length(fn))

do you mean to use

ufn = length(fn) == length(unique(fn))

Guangping,

This works for me:

%%
S.M1 = rand(1,54)
S.M2 = rand(1,91)
S.M3 = rand(1,31)
%%
fS = fieldnames(S);
fl(1)=length(S.(fS{1}));
fl(2)=length(S.(fS{2}));
fl(3)=length(S.(fS{3}));
%%
fn = fieldnames(S);
n = length(fn);
fl = zeros(n,1);
%%
for i=1:n %get each Mi’s length;
    fl(i)=length(S.(fS{i}));
end

I wonder if you have fS defined correctly since you don’t show it.

–loren

1X1 structure S contain M1, M2, M3….M30 which has various length, such as 54, 32, 61…42.
I write code to get the length of each M.
If I write
fl(1)=length(S.(fS{1}));
fl(2)=length(S.(fS{2}));
fl(3)=length(S.(fS{3}));
……….
I will get correct length.
But if I using for loop below, answer is wrong, all equal 0.

fn=fieldnames(S); % all the field name was put into cell fn;
n=length(fn); % get fn length;
for i=1:n %get each Mi’s length;
fl(i)=length(S.(fS{i}));
end

Dear Loren, could you please help me? Why the loop don’t work?

There is nothing ready to go for you, but there are some tools that should make your life easier. ismember is the main one that occurs to me now.

Here I sketch my thought process in how to do this. It might not be the most efficient, but it has all the right steps, I think.

Either know which fields are in common, e.g., .name, or write a little code to find the overlaps. For the overlap ones, you need to get the values for both the first and second structs, and you can then use ismember with multiple outputs to figure out which locations in struct2 match the list in struct1. You can then reorder the struct2 values according to the ismember match indices. You can then delete the matching field (e.g., name) from struct. And finally, merge struct2 into struct1.

Good luck!

–Loren

I’ve got a slight variation on the merger you’ve presented – I want to use a struct like a linked list for merger.

In your example, the heights in s2 are in the same order as the entries of s1. In my problem, I may not know the order of the second structure, and want to use one value as an index to add to the first structure. That is, given a structure that is like this:

s1.name = 'fred';
s1.age = 42;
s1(2).name = 'alice';
s1(2).age = 29;

and a second structure like this:

s2.name = 'alice';
s2.height = 160;
s2(2).name = 'fred';
s2(2).height = 170;

how can I use the name to find the appropriate height to add from s2 to the correct substructure of s1? I ‘d like to end up with a structure like this:

s1.name = 'fred';
s1.age = 42;
s1.height = 170;
s1(2).name = 'alice';
s1(2).age = 29;
s1(2).height = 160;

Is there an easy way to do such a thing?

Yes, I do need to merge structures. I have tried and customised the functions on file exchange but I usually want to merge structures in a very specific way with custom error handling etc.

Mostly I use structures as “contents addressable” containers for data. Such a format makes finding the record easy using dynamic field names in code, and works well for keyboard work (with tab completion).

tmp.age       = 42;
tmp.height    = 170;
mystruc.fred  = tmp;

tmp.age       = 29;
tmp.height    = 160;
mystruc.alice = tmp;

...

name='alice';
mystruc.(name).age

I rarely want to do statistical analysis across the records because I usually want to do computations on the data within the individual record. Structfun can be used to get the items such as the ages into an array.

Regards,
Pete

I recommend you use the link on the right to make the suggestion to Technical Support.

–Loren