addressing array in the function return - matlab

Question

I would like to make the following code simpler.
files=dir('~/some*.txt');
numFiles=length(files);
for i = 1:numFiles
name=files(i).name;
name=strsplit(name,'.');
name=name{1};
name=strsplit(name, '_');
name=name(2);
name = str2num(name{1});
disp(name);
end
I am a begginer in Matlab, in general I would love something like:
name = str2num(strsplit(strsplit(files(i).name,'.')(1),'_')(2));
but matlab does not like this.
Another issue of the approach above is that matlab keeps giving cell type even for something like name(2) but this may be just the problem with my syntax.
Example file names:
3000_0_100ms.txt
3000_0_5s.txt
3000_110_5s.txt
...
Let's say I want to select all files ending in '5s' then I need to split them (after removing the extension) by '_' and return the second part, in the case of the three filenames above, that would be 0, 0, 110.
But I am in general curious how to do this simple operation in matlab without the complicated code that I have above.

Answer 1

Because your filenames follow a specific pattern, they're a prime candidate for a regular expression. While regular expressions can be confusing to learn at the outset they are very powerful tools.
Consider the following example, which pulls out all numbers that have both leading and trailing underscores:
filenames = {'3000_0_100ms.txt', '3000_0_5s.txt', '3000_110_5s.txt'};
strs = regexp(filenames, '(?<=\_)(\d+)(?=\_)', 'match');
strs = [strs{:}]; % Denest one layer of cells
nums = str2double(strs);
Which returns:
nums =
0 0 110
Being used here are what's called lookbehind (?<=...) and lookahead (?=...) operators. As their names suggest, they look in their respective directions related to the expression they're part of, (\d+) in our case, which looks for one or more digits. Though this approach requires more steps than the simple '\_(\d+)\_' expression, the latter requires you either utilize MATLAB's 'tokens' regex operator, which adds another layer of cells and that annoys me, or use the 'match' operator and strip the underscores from the match prior to converting to a numeric value.
Approach 2:
filenames = {'3000_0_100ms.txt', '3000_0_5s.txt', '3000_110_5s.txt'};
strs = regexp(filenames, '\_(\d+)\_', 'tokens');
strs = [strs{:}]; % Denest one layer of cells
strs = [strs{:}]; % Denest another layer of cells
nums = str2double(strs);
Approach 3:
filenames = {'3000_0_100ms.txt', '3000_0_5s.txt', '3000_110_5s.txt'};
strs = regexp(filenames, '\_(\d+)\_', 'match');
strs = [strs{:}]; % Denest one layer of cells
strs = regexprep(strs, '\_', '');
nums = str2double(strs);

Answer 2

You can use regexp to do a regular expression matching and obtain the numbers in the second place directly. This is an explanation of the regular expression I am using.
>>names = regexp({files(:).name},'\d*_(\d*)_\d*m?s\.txt$','tokens')
>>names = [names{:}]; % Get names out of their cells
>>names = [names{:}]; % Break cells one more time
>> nums = str2double(names); % Convert to double to obtain numbers