MatLab - Cellfun where func = strcmp Find where str changes in a cell array

Question

I have a cell array of strings, I want to detect the num of times the string changes and get the indxs for the changes. Given Matlab's cellfun function, I am trying to use it instead of looping. Here is all the code. I appreciate you time, feedback, and comments.

% Cell Array Example
names(1:10)={'OFF'};
names(11:15)={'J1 - 1'};
names(16:22)={'J1 - 2'};
names(23:27)={'J2 - 1'};
names(28)={'Off'};
names=names';

% My cellfun code
cellfun(@(x,y) strcmp(x,y), names(1:2:end),names(2:2:end));

My expected result is a vector of length 27 (length(names)-1), where there are 4 zeros in the vector indicating the strcmp func found 4 cases where the comparison was not equal.

The actual result is a vector of length 14 and has only 2 zeros. I'd really appreciate an explanation, why this unexpected result is occurring.

Thank You

Answer 1

The answer provided by Matt correctly shows the issue with your code. However, you can use strcmp directly because it accepts two cell array of strings as input

>> strcmp(names(1:end-1), names(2:end))
ans =
  Columns 1 through 14
     1     1     1     1     1     1     1     1     1     0     1     1     1     1
  Columns 15 through 27
     0     1     1     1     1     1     1     0     1     1     1     1     0

Answer 2

You could transform the strings into numeric labels using unique, and then apply diff to detect changes:

[~, ~, u] = unique(names);
result = ~diff(u);

Answer 3

If I understand your question correctly, you should be comparing names(1:end-1) with names(2:end). That is, compare string 1 with string 2, compare string 2 with string 3, and so on. You are instead using a stride of 2, comparing string 1 with string 2, string 3 with string 4, and so on. You can fix this by changing your last line to:

cellfun(@(x,y) strcmp(x,y), names(1:end-1),names(2:end))

The result is then:

 Columns 1 through 20:

 1   1   1   1   1   1   1   1   1   0   1   1   1   1   0   1   1   1   1   1

 Columns 21 through 27:

 1   0   1   1   1   1   0