How to substitute numbers in a string with repeated strings?

I have many different strings with different numbers with this format:

 str='A + 2 B -> D + 3 E';

I would like to replace the numbers with repeated strings so I can have

 str='A + B + B -> D + E + E + E';

I did it with so many lines but it looks so ugly and I would like to ask you if you know a better way

Thanks

[Stephen23]

I am sure that this could be done in just one line of code using regexprep and a dynamic replacement string. When I get back to a computer with MATLAB I will give it a try.

Answer 1

[Stephen23]

This is easy with a dynamic regular expression, you can adjust it to suit your needs:

>> str = 'A + 2 B -> D + 3 E';
>> regexprep(str,'(\s+)([+-])\s+(\d+)\s+([A-Z]+)','${repmat([$1,$2,$1,$4],1,str2double($3))}')
ans =
A + B + B -> D + E + E + E

Answer 2

[KL]

something like this?

str={'A + 2 B -> D + 3 E'};
old = {'2', '3'};
new = {'B +','E +'};
for i=1:numel(old)
     str = strrep(str,old(i),new(i))

if you really want to use character array, a little tweak will do,

str=['A + 2 B -> D + 3 E'];
old = {'2', '3'};
new = {'B +','E +'};
for i=1:numel(old)
     str = strrep(str,old{i},new{i})
end
end

As Stephen mentioned, regexprep makes it even more easier without a loop,

str=['A + 2 B -> D + 3 E']
old = {'2', '3'}
new = {'B +','E +'}
newStr = regexprep(str,old,new)

[KL]

You're right Stephen, much simpler with regexprep.

[Stephen23]

@KL: that is not quite what I meant: have a read about dynamic regular expressions:

https://www.mathworks.com/help/matlab/matlab_prog/dynamic-regular-expressions.html

[KL]

ok, sure.

[German Preciat Gonzalez]

Thanks for the feedback, but I would like to apply a script to any formula, not just for the example I showed

Additionally, I would like to repeat the value "3 E" three times as in the example.

Answer 3

[Rik]

My first thought is using repmat, but usually when my first thought is repmat, there is a better solution using sprintf. So someone might have a way faster and more elegant solution than this.

First use isstrprop to figure out the position of the digits ( ind=isstrprop(str,'digit'); ), then loop over the numbers ( for pos=length(find(ind)):-1:1 ) to replicate the correct part.

A more important question is your source. Can you prevent your source to output this format? That would make processing with Matlab less clunky and more clear cut.