Extract numbers from mixed string

K E
2012 7 19
6 个回答
回答已采纳
更新时间：2021 10 21
62 次查看（30 天）

4 个投票

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 个评论
显示 无 隐藏 无

Albert Yam
Albert Yam 2012-7-19
编辑：John Kelly 2015-2-26
What have you tried?
Jianming She
Jianming She 2020-6-17
编辑：Jianming She 2020-6-18
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

请先登录，再进行评论。

请先登录，再回答此问题。

 采纳的回答

Jan
Jan 2012-7-19
编辑：Jan 2012-7-19

19 个投票

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 个评论
显示 1更早的评论 隐藏 1更早的评论

K E
K E 2012-7-19
Lovely, and no regexp required. Lucas, Jan extracts the characters after the Key then gets the first number. From the scanf documentation, the %g format scans in a floating point number.
Jan
Jan 2012-7-19
The removing of the = is clear, I think. Then STRFIND looks for the wanted string. Afterwards the first number behind this string is extracted by SSCANF. Here "behind" means the position, where the string is found plus the number of characters the string have.
Lorenzo
Lorenzo 2013-10-30
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

请先登录，再进行评论。

更多回答（5 个）

Stephan Koehler
Stephan Koehler 2017-6-7

6 个投票

Here is a one-line answer str2num( regexprep( Str, {'\D*([\d\.]+\d)[^\d]*', '[^\d\.]*'}, {'$1 ', ' '} ) )

2 个评论
显示 无 隐藏 无

hi, good answer but how to include the - sign (if present). Thanks.

请先登录，再进行评论。

Freddy
Freddy 2012-7-19

2 个投票

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 个评论
显示 -1更早的评论 隐藏 -1更早的评论

Albert Yam
Albert Yam 2012-7-19
编辑：Albert Yam 2012-7-19
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'.

请先登录，再进行评论。

Albert Yam
Albert Yam 2012-7-19

1 个投票

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 个评论
显示 4更早的评论 隐藏 4更早的评论

K E
K E 2012-7-19
This is very useful for showing how one would construct a regular expression piece by piece. They are so cryptic if you don't use them much.
G
G 2013-11-7
编辑：G 2013-11-7
Be careful with the last solution :
'\d+\.?\d*'
with the case:
teststr = 'Test setup: MaxDistance = 60 m, Rate = 1.000, Permitted Error = .5 Operator Note: Air Temperature=-20 C, Wind Speed 16.375m/s, Altitude 5km (Cloudy)';
it doesn't work (negative number and '.xxx' number notation (like Permitted Error & Air Temperature in the sample)).
If someone has already done these cases ...
G
G 2013-11-7
solved!
regexp(teststr,'\d+\.?\d*|-\d+\.?\d*|\.?\d*','match')
G
G 2013-11-7
编辑：G 2013-11-13
Better:
regexp(teststr,'\d+\.?\d*|-\d+\.?\d*|\.?\d+|-\.?\d+','match')
or
regexp(teststr,'-?\d+\.?\d*|-?\d*\.?\d+','match')
remains the -.34e-004 case !
Angkur Shaikeea
Angkur Shaikeea 2021-10-21
编辑：Angkur Shaikeea 2021-10-21
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?

请先登录，再进行评论。

Dahai Xue
Dahai Xue 2016-3-10
编辑：KSSV 2021-1-25

1 个投票

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
C.J. Harris
C.J. Harris 2012-7-19

0 个投票

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)));

类别

在 帮助中心 和 File Exchange 中查找有关 Characters and Strings 的更多信息

产品

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by