Searching for a string in a very efficient way

Hi.

I have two cell arrays, A and B. A contains 3000 strings and B contains 107,000 strings. Some of the strings in B might also be present in A. Each of these strings is a 7 letter word. I need to find which strings in B are also present in A. I did this by writing the following:

[~,p] = ismember(A, B);
p(p==0) =  []; % removing zeros from the p array

I then use the indices in p to get the strings in B that are also in A. This works but takes a long time to compute (0.4 sec). Since I need to do this step about 30 times (for other A and B), the overall time becomes large. Does anyone have an idea of how to make this string search faster. With thanks in advance, G

Answer 1

[Azzi Abdelmalek]

Instead of ismember(B, A), You should use

ismember(A,B);

[gwar]

In my case ismember(A,B) or ismember(B,A) have very similar computation times. I have edited my question since I mixed up the A and B.

Answer 2

[Jan]

ismember sorts the input strings to allow for an efficient binary search. If you call this 30 times, sorting the larger cell string explicitly will save 29 sorting procedures.

[gwar]

You mean combining all the 30 A´s and 30 B´s and calling ismember only once on the combined cell array?