Generate all possible subset from a character array in MATLAB

I need to generate all possible subset from a character array with reduced execution time. Actual input is of length '500' characters and maximum length of subset is limited to 20 characters.

For example:

input='ABCA';

output ='A', 'B', 'C', 'AB', 'BC', 'CA', 'ABC', 'BCA', 'ABCA'

[madhan ravi]

But you have only 19 in the output?

[Sangeetha R]

example output have 9 subsets with length of characters in the subsets range from 1 to 4. The maximum length of characters in a subset is limited to 20 characters.

[Walter Roberson]

Could you confirm that length(unique(input)) is 500? For example 500 Chinese ideographs? As opposed to length(input) being 500 but the number of unique being much smaller?

[Sangeetha R]

length(input) is 500

Answer 1

[Sangeetha R]

Answer that i found is given below,

tic

input='MERASLIQKAKLAEQAERYEDMAAFMKGAVEKGEELSCEERNLLSVAYKNVVGGQRAAWRVLSSIEQKSNEEGSEEKGPEVREYRVFYLKMKGDYYRYLAEVATGDDKKRIIDSARSAYQEAMDISKKEMPPTNPIRLGLALNFSVFHYEIANSPEEAISLAKTTFDEAMADLHTLSEDSYKDSTLIMQLLRDNLTLWTADNAGEEGGEAPQEPQSMERASLIQKAKLAEQAERYEDMAAFMKGAVEKGEELSCEERNLLSVAYKNVVGGQRAAWRVLSSIEQKSNEEGSEEKGPEVREYRVFYLKMKGDYYRYLAEVATGDDKKRIIDSARSAYQEAMDISKKEMPPTNPIRLGLALNFSVFHYEIANSPEEAISLAKTTFDEAMADLHTLSEDSYKDSTLIMQLLRDNLTLWTADNAGEEGGEAPQEPQSSEDSYKDSTLIMQLLRDNLTLWTADNAGEEGGEAPQEPQSMERASLIQKAKLAEQAERYEDMAAFMKGAVEKGEELSCEERNLLSVAYKNVVGGQRAAW';

l=length(input);

begn=1;

count=1;

output_seq=cell(1000,1);%preallocating

for i=1:l

if(begn<=l)

[count,output_seq]=pep(begn,l,input,count,output_seq);

begn=begn+1;

end

end

output_unique=unique(output_seq);

toc

function [count,output_seq]=pep(b,l,input,count,output_seq)

for i=0:l

if(b+i-b<21)

if(b+i<=l)

p = input(b:b+i);

output_seq{count}=p;

count=count+1;

end

end

end

end

Answer 2

[Walter Roberson]

Consider

[S(1:end-2);
 S(2:end-1);
 S(3:end)].'

Now unique rows