Extracting numbers from mixed string

Question

pink flower 2020-9-20

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/596659-extracting-numbers-from-mixed-string

评论： Ameer Hamza 2020-9-20

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!

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Matt J 2020-9-20

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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 2020-9-20

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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

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Answer 1

Ameer Hamza 2020-9-20

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https://ww2.mathworks.cn/matlabcentral/answers/596659-extracting-numbers-from-mixed-string#answer_497353

编辑：Ameer Hamza 2020-9-20

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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};

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pink flower 2020-9-20

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 2020-9-20

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.

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Answer 2

Star Strider 2020-9-20

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/596659-extracting-numbers-from-mixed-string#answer_497359

编辑：Star Strider 2020-9-20

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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"