Question

I am relatively new to Matlab and have a question about creating a logical array in Matlab
Suppose I have the following data. A contains actual values and B column denotes U as undetected

A B

2 U

4 U

5

6 U

6

7 U

8

I would like to create a logical array such as undetected values get a 1 and else 0. Thus the c column would look some thing like this:

C = 1 1 0 1 0 1 0

Thank you for your help.

Answer 1

If your input is a cell array (we’ll call it data), then I typically use cellfun for this sort of work.

C = cellfun(@(x) ~isempty(x) && ischar(x) && strcmp(x,'U') , data(:,2))

This defines an anonymous function which returns true for any input which is (1) not empty, (2) a character array and (3) has a value of ‘U’ and. It calls that function on each element in the second column of data, and returns it in an array C.

I like that it fits a single operation on a single line. It is easy to read after you use the construction enough times (but perhaps not easy to read the first few times).

---

A more typical (and perhaps easier to understand) solution is to use a loop.

 C = logical(zeros(size(data,1),1));  %Always preallocate your results vector
 for ix = 1:size(data,1)
     curValue = data{ix,2}l
     C(ix) =  ~isempty(curValue ) && ischar(curValue ) && strcmp(curValue ,'U');
 end

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Finally, it sounds like you may actually want your result back in your original cell array, in the third column. That is a small change to the loop above, like so:

 for ix = 1:size(data,1)
     curValue = data{ix,2};
     data{ix,3} =  ~isempty(curValue) && ischar(curValue) && strcmp(curValue ,'U');
 end

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EDIT

If your data is in a cell array of arrays (based on a recent comment), then try:

C = mydata{2} == 'U';

This extracts the character array, and compares each element to the character 'U'.