Extracting numbers from mixed string

I need to extract the four-digit information that is before the period. With these commands that I have, only the zero digit comes out. How can I proceed to obtain the 4 zero digits?

str = 'preci_CZ_02000_20200101_0000.txt';
out = extractBetween(str,25,28);

Thanks!

[Matt J]

That's not what I get. I get all four digits.

>> str = 'preci_CZ_02000_20200101_0000.txt';
out = extractBetween(str,25,28)

out =

  1×1 cell array

    {'0000'}

[pink flower]

I'm actually trying to do it inside a loop, because I need to extract from several files.

   for x = 1:length(ix20); 
        
        namex = files(i).name;
        sss = extractBetween(namex,25,28);
        hm(x)=string(sss);
        
   end

Answer 1

[Ameer Hamza]

Your current code will only work if all the strings have equal length.

For a general case, try using regex

str = 'preci_CZ_02000_20200101_0000.txt';
out_str = regexp(str, '\_([0-9]{4})\.', 'tokens');
out_str = out_str{1}{1};

[pink flower]

I tried but I couldn't. I'm actually trying to do it inside a loop, because I need to extract from several files.

  for x = 1:length(ix20); 
        
        str = files(i).name;
        out_str = regexp(str, '\_([0-9]{4})\.', 'tokens');
        out_str = out_str{1}{1};
        hm(x)=string(out_str);
        
    end

And then I need to leave this as a double.

[Ameer Hamza]

What is the error? You can use str2num() to convert the values to numeric format.

[pink flower]

There is no error, but I cannot leave the 4 digits together when there is 0000, 0010, 0020,0030, for example. I don't know what to do anymore!

[Ameer Hamza]

I didn't understand the problem. Can you show how do you want to use the output. That will be helpful in suggesting a solution.

Answer 2

[Star Strider]

Another approach:

str = 'preci_CZ_02000_20200101_0000.txt';
out = regexp(str, '(?:\d{4})\>','match');

producing:

out =

  1×1 cell array

    {'0000'}

EDIT — (20 Sep 2020 at 4:40)

I do not have ‘files.name’, however this approach works and is efficient:

str = compose('preci_CZ_02000_20200101_%04d.txt', 0:5:20).'                 % Create File Vector
out = regexp(str, '(?:\d{4})\>','match');                                   % Extract Last Four Digits Before Dot
hm = string([out{:}]).'                                                     % Display Results

producing:

str =

  5×1 cell array

    {'preci_CZ_02000_20200101_0000.txt'}
    {'preci_CZ_02000_20200101_0005.txt'}
    {'preci_CZ_02000_20200101_0010.txt'}
    {'preci_CZ_02000_20200101_0015.txt'}
    {'preci_CZ_02000_20200101_0020.txt'}

hm = 

  5×1 string array

    "0000"
    "0005"
    "0010"
    "0015"
    "0020"

.

[Star Strider]

Note: My code here was quoted in: How can I to convert a cell to a double without losing the leading zeros?

Answer 3

[Mario Malic]

Variable str is actually a char array, you can get last 4 characters before dot by

newstr = str(end-7:end-4)

To get it in double, you can use str2num function.