Extract numbers from mixed string

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K E
K E on 19 Jul 2012
Edited: Angkur Shaikeea on 21 Oct 2021
I have a file containing header lines like the following,
Test setup: MaxDistance = 60 m, Rate = 1.000, Permitted Error = 50
Operator Note: Air Temperature=20 C, Wind Speed 16.375m/s, Altitude 5km (Cloudy)
For a given parameter such as MaxDistance or Wind Speed, I would like to extract its numerical value. This is tricky because sometimes there is an equal sign, space, or units, and sometimes there is not, because different operators enter their notes differently (lesson: next time enforce consistency).
How would I extract the following: All numerical characters (ignoring spaces and equal signs but keeping decimal points) that appear after the string representing the parameter name. Stop when a letter or punctuation mark is reached. In the case of 'MaxDistance', I would obtain 60. In the case of Wind Speed, I would obtain 16.375.
  2 Comments
Jianming She
Jianming She on 17 Jun 2020
Edited: Jianming She on 18 Jun 2020
This seems a more general way:
function numArray = extractNumFromStr(str)
str1 = regexprep(str,'[,;=]', ' ');
str2 = regexprep(regexprep(str1,'[^- 0-9.eE(,)/]',''), ' \D* ',' ');
str3 = regexprep(str2, {'\.\s','\E\s','\e\s','\s\E','\s\e'},' ');
numArray = str2num(str3);
Example:
a = 'alpha=-3.5,beta=1e-2. but gamma = -34.1'
numArray = extractNumFromStr(a)
numArray =
-3.5000 0.0100 -34.1000

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Accepted Answer

Jan
Jan on 19 Jul 2012
Edited: Jan on 19 Jul 2012
Import the file into a string at first, e.g. by fileread. Then you get something like this (if not, please explain all necessary details):
Str = ['Test setup: MaxDistance = 60 m, Rate = 1.000, ', ...
'Permitted Error = 50 Operator Note: Air Temperature=20 C, ', ...
'Wind Speed 16.375m/s, Altitude 5km (Cloudy)'];
Now omit all equal characters:
Str(strfind(Str, '=')) = [];
Finally you can get the values:
Key = 'MaxDistance';
Index = strfind(Str, Key);
Value = sscanf(Str(Index(1) + length(Key):end), '%g', 1);
"Index(1)" cares for multiple occurences of the key.
  3 Comments
Lorenzo
Lorenzo on 30 Oct 2013
This works great! Just a quick question Jan: what if you want to find all the uccurrence of a numeric value between two strings? For instance, let's say you want the numeric values that can be found between MaxDistance and Altitude in the original example (i.e. 60, 1000, 50 ecc ecc...). How can you achieve that?
I tried this:
Key1 = 'MaxDistance'; Key2 = 'Altitude'; Index1 = strfind(file, Key1); Index2 = strfind(file, Key2); Value = sscanf(file(Index1:Index2), '%g',1);
but still I can get nothing but the first value.... Also, I dont know a-priori the number of numbers that can be encontured between the two strings...
Thanks!
Lorenzo

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More Answers (5)

Stephan Koehler
Stephan Koehler on 7 Jun 2017
Here is a one-line answer str2num( regexprep( Str, {'\D*([\d\.]+\d)[^\d]*', '[^\d\.]*'}, {'$1 ', ' '} ) )
  2 Comments
Marco A. Acevedo Z.
Marco A. Acevedo Z. on 2 Apr 2021
hi, good answer but how to include the - sign (if present). Thanks.

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Freddy
Freddy on 19 Jul 2012
Maybe a little bit too late, but i like to present you also my ("regexp training"-) solution. :)
A = regexp(Str,'(?<Keyword>(?:\w+\s*\w+))\s*=?\s*(?<Value>\d+\.?\d*)','names');
s = struct();
for i = A,
s.(genvarname(i.('Keyword'))) = str2double(i.('Value'));
end
  1 Comment
Albert Yam
Albert Yam on 19 Jul 2012
Edited: Albert Yam on 19 Jul 2012
That took a long time for me to understand what you are doing. That's cool though.
How does it skip over 'Operator Note:' ?
Edit: Never mind I get it. It doesn't have anything for ':'. The '(?:\w' has nothing to do with a ':' in the string, it is grouping the token for 'up to two words'.

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Albert Yam
Albert Yam on 19 Jul 2012
This is how I went about it, all steps included even the errors.
teststr = 'Test setup: MaxDistance = 60 m, Rate = 1.000, Permitted Error = 50 Operator Note: Air Temperature=20 C, Wind Speed 16.375m/s, Altitude 5km (Cloudy)';
regexp(teststr,[\d])
regexp(teststr,['\d'])
regexp(teststr,['\d'],'match')
regexp(teststr,['\d+'],'match')
regexp(teststr,['\d+.?'],'match')
regexp(teststr,['\d+\.?'],'match')
regexp(teststr,['\d+\.?\d?'],'match')
regexp(teststr,['\d+\.?\d+?'],'match')
regexp(teststr,['\d+\.?\d*?'],'match')
regexp(teststr,['\d+\.?\d?'],'match')
regexp(teststr,['\d+\.?\d*'],'match')
  6 Comments
Angkur Shaikeea
Angkur Shaikeea on 21 Oct 2021
Edited: Angkur Shaikeea on 21 Oct 2021
i need to extract
0.00000 0.00000 0.00000
0.00000 1.00000 0.00000
1.00000 0.00000 0.00000
from a text file containing
.............................................
Nodal positions:
0.00000 0.00000 0.00000
0.00000 1.00000 0.00000
1.00000 0.00000 0.00000
Nodal positions:
0.00000 0.00000 0.00000
0.00000 1.00000 0.00000
1.00000 0.00000 0.00000
Nodal positions:
0.00000 0.00000 0.00000
0.00000 1.00000 0.00000
1.00000 0.00000 0.00000
any help using regexp?

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C.J. Harris
C.J. Harris on 19 Jul 2012
In order to extract a certain value:
Str = ['Test setup: MaxDistance = 60 m, Rate = 1.000, ', ...
'Permitted Error = 50 Operator Note: Air Temperature=20 C, ', ...
'Wind Speed 16.375m/s, Altitude 5km (Cloudy)'];
matchWord = 'Air Temperature';
[a,b] = regexp(Str,'\d+(\.\d+)?');
strPos = find(a > strfind(Str,matchWord),1,'first');
nValue = str2double(Str(a(strPos):b(strPos)));

Dahai Xue
Dahai Xue on 10 Mar 2016
Edited: KSSV on 25 Jan 2021
C.J. Harris, I put your regexp into a function to extract all numbers using regexp. I have hard time to find an array operation that can use the 'a' and 'b' without the loop. Hopefully somebody has ideas. Of course it is not difficult to add more parameters or options to find "certain" numbers with preceding or following landmark strings.
function nums = regExtractNums(str)
[a,b] = regexp(str, '\d+(\.\d+)?');
nums = zeros(length(a),1);
for k = 1:length(a)
nums(k) = str2double(str(a(k):b(k)));
end
end

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