How do I use matlab ismember in data structures with multiple nested fields?

Question

In matlab I have the following 2 data structures b and c defined as follows.

b(1).b = struct('c',{'a', 'b', 'c'})
c(1).b = struct('c',{'b', 'a', 'c'})

Now I want to use ismember to find out if the elements of b(1).b.c are contained in c(1).b.c and if so, which indices of c(1).b.c each of the elements belong to.

For example: b(1).b(1).c = a, I want to backtrace this to structure c to find which index of structure c 'a' belongs to (it should return 2 since 'a' is the second element of structure c).

I have tried

[~, ind] = ismember({b(1).b.c},{c(1).b.c})

which has worked for me previously with a different data structure but I now receive the following error:

*Error using cell/ismember>cellismemberR2012a (line 192)
Input A of class cell and input B of class cell must be cell arrays of      strings, unless one is a string.
Error in cell/ismember (line 56)
[varargout{1:max(1,nargout)}] = cellismemberR2012a(A,B);*

I am not sure why its not working. Does anybody know how to fix this? Thanks.

Using your exact code in R2011a (Version 7.12.0.635) works as you expect giving [2 1 3]. What version of Matlab are you using? — TallBrianL, Mar 06 '15 at 02:10
Fine in 2012b as well. Are there any other variables in your Matlab workspace that might be conflicting? (For example, is there already a structure `b`?) — David, Mar 06 '15 at 02:26
According [this similar](http://stackoverflow.com/questions/27227291/matlab-why-ismember-does-not-work) (duplicate?), the error arises when the data is not homogeneous. Is the sample given the actual set of data generating the error? — TroyHaskin, Mar 06 '15 at 03:17
@TroyHaskin nope this is not the data set, I can't provide the original data set because its huge so I made one up with a similar structure... — Maheen Siddiqui, Mar 06 '15 at 08:43
@MaheenSiddiqui Is all of your data of the same type and non-empty? — TroyHaskin, Mar 06 '15 at 13:29
@TroyHaskin yup its all the same and non-empty... I have found a solution, I'll post it in the answer. — Maheen Siddiqui, Mar 06 '15 at 14:40

score 0 · Answer 1 · answered Mar 06 '15 at 02:33

0

Googling around did not show any possible solutions but there are couple options:

[~, ind] = ismember([{b(1).b.c}],[{c(1).b.c}])

and casting to cell array:

[~,idx]=ismember(struct2cell(b(1).b),struct2cell(c(1).b))
idx=reshape(idx,1,3);

For both output should be:

2 1 3

answered Mar 06 '15 at 02:33

madbitloman

816
2
13
21

I still get the same error... and using struct2cell I get the error `Undefined function 'struct2cell' for input arguments of type 'cell'.` – Maheen Siddiqui Mar 06 '15 at 08:48

score 0 · Accepted Answer · answered Mar 06 '15 at 14:44

I found the following to work.

First assigning b(1).b.c to an array S and then comparing that with the data structure c using ismember.

S = [b(1).b.c]
S = S'
[~, ind] = ismember(S,{c(1).b.c})

I have found this to work.

Also,

[~, ind] = ismember([b(1).b.c}],[c(1).b.c])

does not give an error but all the values in ind are zero which is not true for the data.

Thanks all for your input!

How do I use matlab ismember in data structures with multiple nested fields?

2 Answers2