Create a row vector comparing strings in a for loop

I have two string arrays with different sizes and assume that the second one (s2) has a variable size.

I need to create a vector (index) that contains only the indices where 'strcmpi' returns the logical value 1. It works if 's2' contains only strings present in 's1', otherwiswe the following error occurs. I think that's because I am assigning to 'index' the size of 'k' but there will be only 3 logical value = 1, but I don't know how to fix it.

Any help would be appreciated. Thanks.

s1 = { 'FMO1','FMO2','FMO3','FMO4', 'BAO1', 'BAO2', 'BAO3', 'BAO4'};
s2 = {'mean','FMO1','BAO4','FMO2'}; 

for k = 1 : length(s2)
    compare = strcmpi(s2{k},s1);
    index(k) = find(compare==1)   
end

Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.

[Lorenzo Amedeo]

Also thanks to you, do I have to accept your answer too? even if I already accepted the previous one

Answer 1

[Davide Masiello]

index = [];
s1 = { 'FMO1','FMO2','FMO3','FMO4', 'BAO1', 'BAO2', 'BAO3', 'BAO4'};
s2 = {'mean','FMO1','BAO4','FMO2'}; 
for k = 1 : length(s2)
    compare = strcmpi(s2{k},s1);
    index = [index,find(compare==1)];   
end
index

index = 1×3

1 8 2

This way, even if any of the entry in s2 appears several times in s1 you should be ok.

[Lorenzo Amedeo]

Problem solved, thanks.

[Stephen23]

Expanding the output array will be inefficient.

Answer 2

[Stephen23]

The simple MATLAB approach:

s1 = { 'FMO1','FMO2','FMO3','FMO4', 'BAO1', 'BAO2', 'BAO3', 'BAO4'};
s2 = {'mean','FMO1','BAO4','FMO2'};
X = contains(s1,s2)

X = 1×8 logical array
   1   1   0   0   0   0   0   1

Y = find(X) % optional

Y = 1×3

1 2 8

[Lorenzo Amedeo]

Thank you, I would accept your answer but I don't think I can accept more than one.