Extracting string and number pairs from a mixed string
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Dear all,
I have read in material data and have gotten an array of chemical compositions of the type (chr):
'Fe61Zr8Co7Mo15B7Y2' sometimes even '(Fe0.5Co0.5)58.5Cr14Mo6C15B6Er0.5' wherein Fe and Co have a percentage of 29.25 (58.5*0.5...).
How do I extract the chemical composition so that I receive an array (or two) like
['Fe', 'Zr', 'Co', 'Mo', 'B', 'Y'; 61, 8, 7, 15, 7, 2]?
I am somehow failing to use sscanf correctly, e.g. numbers = sscanf('Fe61Zr8Co7Mo15B7Y2', '%f') won't do anything since I need to omit varying strings :(
Thanks a lot in advance!
Greetings
Lukas
Accepted Answer
The two lines marked with %%% are used to convert substrings like '(Fe0.5Co0.5)58.5' into 'Fe29.25Co29.25', after which the designator+number matching and extraction is easy:
>> str = '(Fe0.5Co0.5)58.5Cr14Mo6C15B6Er0.5';
>> baz = @(s,b)regexprep(s,'(\d+\.?\d*)','${num2str(str2double($1)*str2double(b))}'); %%%
>> tmp = regexprep(str,'\((([A-Z][a-z]*\d+\.?\d*)+)\)(\d+\.?\d*)','${baz($1,$2)}'); %%%
>> out = regexp(tmp,'([A-Z][a-z]*)(\d+\.?\d*)','tokens');
>> out = vertcat(out{:})
out =
'Fe' '29.25'
'Co' '29.25'
'Cr' '14'
'Mo' '6'
'C' '15'
'B' '6'
'Er' '0.5'
>> str2double(out(:,2)) % optional
ans =
29.25
29.25
14
6
15
6
0.5
The code uses two layers of dynamic regular expression, the first calls baz for each each '(AxBy...)N' substring, then inside baz each of x, y, etc. is multiplied with N. The result is converted to char for reinsertiion.
6 Comments
LukasJ
on 14 Feb 2020
"2nd line creates a function, baz, with the variables (s,b), I guess"
Yes, it defines an anonymous function with two input arguments:
"Then baz is called in executing regexprerp again?"
The function |baz| is called by |regexprep| on the third line. For your example string its two inputs will be 'Fe0.5Co0.5' and '58.5'.
"Is there any tutorial I could use, to be able to write code like this myself?"
Read the documentation, try the examples.
"Regexp and regexprep appear to be very powerful but the inputs look kind of chaotic"
Regular expressions are a language unto themselves. They require practice and reading the documentation again and again and again and again and again...
In this case I also used dynamic regular expressions to call |baz| and to recalculate those numeric values:
Here is a breakdown of the regular expressions:
'(\d+\.?\d*)' % match integer or decimal number
( % start group 1
\d+ % one or more digits
\.? % optional period character
\d* % zero or more digits
) % end group 1.
'\((([A-Z][a-z]*\d+\.?\d*)+)\)(\d+\.?\d*)' % match e.g. '(Fe0.5Co0.5)58.5' % FIXED
\( % literal left parenthesis
( % start group 1
( % start group 0
[A-Z] % match one A-Z character
[a-z]* % match zero or more a-z characters
\d+\.?\d* % like 1st regex, match integer or decimal % FIXED
)+ % one or more of group 0
) % end group 1
\) % literal right parenthesis
( % start group 2
\d+\.?\d* % like 1st regex, match integer or decimal
) % end group 2
'([A-Z][a-z]*)(\d+\.?\d*)' % match e.g. 'Cr14' or 'Fe29.25'
( % start group 1
[A-Z] % match one A-Z character
[a-z]* % match zero or more a-z characters
) % end group 1
( % start group 2
\d+\.?\d* % like 1st regex, match integer or decimal
) % end group 2
You can see that the regular expressions always match the numbers and the element symbols in the same way, just group them in slightly different ways. The groups are referred to using |$1| and |$2| in the replacement expressions.
You might also like to download my interactive tool IRGEXP:
LukasJ
on 14 Feb 2020
LukasJ
on 15 Jun 2020
The reason is that I missed a question mark here:
tmp = regexprep(str,'\((([A-Z][a-z]*\d+\.?\d*)+)\)(\d+\.?\d*)','${baz($1,$2)}')
% ^ missing
which meant that the regular expression did not match integer numbers, only numbers with a decimal point.
With that question mark in place (I have now corrected the question and comments), this is the output:
>> out = regexp(tmp,'([A-Z][a-z]*)(\d+\.?\d*)','tokens');
>> out = vertcat(out{:})
out =
'Fe' '6550.4'
'B' '2208'
'Y' '441.6'
'Nb' '8'
"Another issue are compositions which contain more "subcompositions" and are separated by other brackets."
Regular expressions alone are not really suitable for this. For parsing arbitrarily nested brackets like that you will probably have to write your own string parser, e.g. based on a recursive function which uses regular expressions or other string manipulation inside it. Have you worked with recursive functions before?
Чебура́шка, да!
More Answers (1)
LukasJ
on 13 Feb 2020
0 votes
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