How do I extract number from file name?

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Emmanuel 2017-3-2

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编辑： Stephen23 2017-3-2

My file names are like 1443242345.88.png,1232342.45.png. I want these numbers of the file name and extract them as integers like 1443242345.88, 1232342.45 and use them for mathematical operations.

How do I do it with regexp or any other method?

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Stephen23 2017-3-2

1443242345.88 is not an integer.

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Answer 1

Emmanuel 2017-3-2

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So, this works: if A is 1443242345.88.png

 A = A(1:end-4)
 At = str2num(A)

gives numeric value of A which is 1443242345.88

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Stephen23 2017-3-2

编辑：Stephen23 2017-3-2

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It would be better to use str2double, because this avoids the slow eval inside str2num and gives predictable output with non-number input strings:

At = str2double(A)

and also your code does not take into account the fact that file extensions are not always the same length, e.g. .m, .jpeg, etc. A much more robust solution is to use fileparts, which will always split this correctly:

 [P,N,E] = fileparts(A);
 V = str2double(N);

You also might like to consider Guillaume's very nice answer with regexp.

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Answer 2

Guillaume 2017-3-2

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编辑：Guillaume 2017-3-2

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An integer is a number with no fractional part so 1443242345.88 is not an integer.

numbers = str2double(regexp(filenames, '\d+\.\d+', 'match', 'once'))

will extract the numbers as double and assumes that all numbers have a dot in them

tokens = regexp(filenames, '(\d+)\.(\d+)', 'tokens', 'once');
numbers = str2double(vertcat(tokens{:}))

will extract the numbers on each side of the dots as a two column matrix of integers.

Note: and either will work will a cell array of filenames, so you can do the conversion in one go for ALL your files unlike your solution which you accepted when I was writing mine.

Note 2: and because I use str2double instead of str2num, the solution doesn't risk executing arbitrary code.