MATLAB: Append a char vector to a subset of cells (whose indices are known) in cell array of character vectors

Question

Hello MATLAB community:

I am trying to determine the most effective way of going about the following task. I have a cell array of character vectors: mycell = {'cal_start', 't_001', 't_002', …, 't_200', 'cal_end', 'exp_start', 't_001', 't_02' ,…, 't_048', 'exp_end'};

I have defined the relevant indices from this cell array, the contents of which I would like to append a character vector. In fact there are two index ranges I have defined, and these index ranges indentify the cells between 'cal_start" and 'cal_end', and 'exp_start' and 'exp_end'.

For example:

% regarding the below, for context, 't' is trial, 'cal' is calibration, 
% and 'exp' is experiment.
mycell = {'cal_start', 't_001', 't_002', 't_003', 't004', 'cal_end', 'exp_start',...
    't_001', 't_002', 'exp_end'}; 
a = find(contains(mycell, 'cal'));
% i.e., a = [1,6]
b = find(contains(mycell, 'exp'));
% i.e., b = [7,10]
% define trial indices comprising the calibration phase 
calidx_rng = a(1)+1 : a(2)-1;
% define trial indices comprising the experiment phase 
expidx_rng = b(1)+1 : b(2)-1;

Now, for the charcater vectors of mycell contained in calidx_rng, I want to append 'cal_' at the beginning of each, such that you now have:

mycell = {'cal_start', 'cal_t_001', 'cal_t_002', cal_t_003', cal_t_004', 'cal_end', 'exp_start', 't_001', 't_002', 'exp_end'}

And, similarly, I want to perform the "same" operation, but appending 'exp_' to mycell(expidx_rng) so that the final product is:

mycell = {'cal_start', 'cal_t_001', 'cal_t_002', cal_t_003', cal_t_004', 'cal_end', 'exp_start', 'exp_t_001', 'exp_t_002', 'exp_end'};

Sorry, there was a premature submission when I was adding tags, to finish my post, this is what I have attempted (though here I am continuing in the context of the simplified example above):

mynewcell = append('cal_', mycell(calidx_rng));

MATLAB gives ther error:

Wrong number of input arguments for obsolete matrix-based syntax.

My suspicion is that the best way to approach this is using the cellfun or arrayfun functions, but I must admit, the examples provided in the documentation don't give me a clear picture as to how I should use them in my case.

This is probably a stupid question, but thanks for your time.

Answer 1

Your basic concept is correct, you just need to use indexing on the LHS as well as the RHS:

mycell(calidx_rng) = strcat('cal_', mycell(calidx_rng));
mycell(expidx_rng) = strcat('exp_', mycell(expidx_rng));
%     ^^^^^^^^^^^^ you need this!

Giving:

>> mycell{:}
ans = cal_start
ans = cal_t_001
ans = cal_t_002
ans = cal_t_003
ans = cal_t004
ans = cal_end
ans = exp_start
ans = exp_t_001
ans = exp_t_002
ans = exp_end