# Extracting numbers from mixed string

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pink flower on 20 Sep 2020
Commented: Ameer Hamza on 20 Sep 2020
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 on 20 Sep 2020
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 on 20 Sep 2020
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

Ameer Hamza on 20 Sep 2020
Edited: Ameer Hamza on 20 Sep 2020
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};

Show 1 older comment
Ameer Hamza on 20 Sep 2020
What is the error? You can use str2num() to convert the values to numeric format.
pink flower on 20 Sep 2020
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 on 20 Sep 2020
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.

Star Strider on 20 Sep 2020
Edited: Star Strider on 20 Sep 2020
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"
.

#### 1 Comment

Star Strider on 20 Sep 2020

Mario Malic on 20 Sep 2020
Edited: Mario Malic on 20 Sep 2020
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.