finding instances of a string withinin a structure

Dear community,

I have structure which I would like to locate the instances of a certain string. The data is laid out as follows:

The variable is called

Markers which is 360x24 struct , with five fields.

The fields are:

ChannelNumber (double)

Description (which is a character/string)

Points (double)

Position (double)

Type (character/string)

Example:

What I'm trying to do is to find the index of all instances of 's2' in Description, so it's a string. I've tried modifying code which I've found on here, but it doesn't seem to work.

Just to give another example of the file layout, if I click on one of the structs containing S2 it looks like this in the workspace:

Markers(2, 2).Description

I know I need to use strcmp of strfind, but I just don't seem to be able to get the syntax right. Generally I never work with anything other than matrixes or cells, so this is a bit beyond my experience!

Hopefully someone can help please?

Best wishes, Joe

Answer 1

[Jan]

match = reshape(strcmp({Markers.Description}, 's2'), size(Markers));

Now match(i,j) is TRUE, when the struct Markers(i,j).Description is the string 's2'. If any occurrence is wanted, e.g. also "*s2*", you need:

Desc   = {Markers.Description};
Desc(~cellfun('isclass', Desc, 'char')) = {''};  % Care for non-strings
matchC = reshape(strfind(Desc, 's2'), size(Markers));
match  = ~cellfun('isempty', matchC);

Now match is again a logical matrix, which is TRUE, when the corresponding field contains the string 's2' anywhere.

[Joe Butler]

Thank you for taking the time to answer. In each row/vector there should be only one instance of s2 (and other various markers I need to add - some similar in name like s20 etc) so the code you offered was helpful for getting me to achieve what I wanted

Just for reference in order to help others with what I've used it for, I then, with your solution, used the following code to access the times associated with S2 onset.

match = reshape(strcmp({Markers.Description}, 's2'), size(Markers));

 S2_marker_times = vertcat(Markers(match).Position);

Thanks again, Joe

Answer 2

[Ameer Hamza]

The following will return a boolean array of the indexes to indicate which struct contains the required string

indexes = reshape(contains({Markers.Description}, 's2'), size(Markers))
Markers(indexes) % will return the structs containing 's2' in Description

If you are interested in the actual location of 's2' inside each string, use

reshape(strfind({Markers. Description}, 's2'), size(Markers))

[Joe Butler]

Hi, thanks - although I try your code and I get the following error (which is the same error I got when modifying others' code):

Error using strfind Cell must be a cell array of character vectors.

In case I've described it wrong, an image of the data is thus:

Also not sure if it matters, but sometimes the Description fields are empty?

The aim is to use these indices to then extract the numbers from Position and place these into a matrix of the same length as the struct.

Thanks again,

Joe

[Ameer Hamza]

If some description field is empty matrices [], then it will create the problem. In this case, try following

positions = arrayfun(@(x) strfind(x.Description, 's2'), Markers, 'UniformOutput', false)
boolIndex = arrayfun(@(x) ~isempty(strfind(x.Description, 's2')), Markers)

[Joe Butler]

Thanks this was helpful!