Edit user input

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Raldi 2011-12-1

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https://ww2.mathworks.cn/matlabcentral/answers/22839-edit-user-input

Lets say i have something like s='12s+34a+45'; Is there a way so i can only store the numbers that are in front of the letter s and store it to an array?

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Answer 1

Walter Roberson 2011-12-1

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https://ww2.mathworks.cn/matlabcentral/answers/22839-edit-user-input#answer_30022

在 MATLAB Online 中打开

numstrs = regexp(TheString, '-?\d+(?=\s*s)', 'match');

and convert the resulting cells strings in to numeric forms.

The (?=\s*s) part is regexp-ese for "the expression after the '=' until the ')' must be matched in the input right after whatever was matched before this, but do not return this part as part of the match". Another way of phrasing this is that it "looks ahead" for the pattern but does not include it as part of what is matched.

\s*s stands for "any number of whitespace characters (including none), followed by the letter 's')

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Raldi 2011-12-1

Thanks Walter. This is way much better than what i came up with

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Answer 2

Raldi 2011-12-2

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https://ww2.mathworks.cn/matlabcentral/answers/22839-edit-user-input#answer_30095

There is a problem though with this code. It seems it wont recognise lets say 0.5*s but it will only take number 5, so i need a way to exclude '.' from regexp.

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Walter Roberson 2011-12-2

If you define exactly which patterns of characters are to be accepted, then a regexp() expression can be constructed. The pattern to match a general floating point number that might be in exponential form gets quite complicated though.

numstrs = regexp(TheString, '-?(?:(?:\d*\.)?\d+|\d+\.)(?=\s*s)', 'match')

The above does not recognize exponentials, but it does recognize

optional leading minus sign, recognizes digits followed by 's', recognizes digits followed by '.s', recognizes digits followed by '.' followed by digits followed by 's', recognizes '.' followed by digits followed by 's', while still refusing '.s' alone with no digits. Oh yes, optional spaces are permitted before the 's' itself.

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