CODEWITHSUNDEEP
regexmatlab
abscissa
abscissa

Reputation: 245

Replacing strings with regexprep inside a for loop? (MATLAB)

I've been having a lot of trouble with programmatic find and replace, in Matlab. I have reproduced a MWE here.

Say I have the following code in a textfile called 'BaseJac3.txt':

x2 = -S1_2*(r1+a*K+a*P)+k*KS1_1+d*(PS1_1+KS1_2);
x3 = -S1_3*(r1+a*K+a*P)+k*KS1_2+d*(PS1_2+KS1_3);
x4 = -S1_4*(r1+a*K+a*P)+k*KS1_3+d*(PS1_3+KS1_4);
x5 = -S1_5*(r2+a*K+a*P)+k*KS1_4+d*(PS1_4+KS1_5);

I need to replace

S1_2 with y(2), ... , S1_5 with y(5);

KS1_1 through KS1_5 with y(52) to y(57)

PS1_1 through PS1_4 with y(102) to y(105)

How can I do this? I've tried using this: http://www.mathworks.com/matlabcentral/fileexchange/42877-find-and-replace-in-files

and also my following code:

text1 = fileread('BaseJac3.txt');

for k = 1:4
    regexprep(text1,['PS1_' num2str(k)],['y(' num2str(k+101) ')']);
end
for k = 1:5
    regexprep(text1,['KS1_' num2str(k)],['y(' num2str(k+51) ')']);
end
for k = 2:5
    regexprep(text1,['S1_' num2str(k)],['y(' num2str(k) ')']);
end

but neither seems to be working properly. I'm not sure about regular expressions.

Thanks in advance for help.

Upvotes: 2

Views: 277

Answers (2)

sco1
sco1

Reputation: 12214

Some regex whiz can probably work up a way to do this all in one shot, but for clarity I've split it into 3 passes. regexprep works on cell arrays of strings so you can pass it the entire array at once.

function newstr = testcode(str)
helper = @(x,y) num2str(str2double(x) + y);  % Generate anonymous function for our dynamic regexrep expression

pass1 = regexprep(str, '(?<!(K|P))S1_(\d*)', 'y($1)');  %S1
pass2 = regexprep(pass1, 'KS1_(\d*)', 'y(${helper($1,51)})');  % KS1
pass3 = regexprep(pass2, 'PS1_(\d*)', 'y(${helper($1,101)})');  % PS1
newstr = pass3;
end

What I've done here is utilize regexprep's Tokens and Dynamic Expressions to format the output.

Pass 1 works on S1, and uses a lookbehind assertion to ignore KS1 and PS1. The expression matches the digit following S1_ and uses it as the token for y().

Passes 2 and 3 work on KS1 and PS1. These use the same token approach for the match but also use a dynamic expression for the replacement. These allow us to pass a token to any MATLAB function that returns a string, and uses that string as the replacement. I've defined a helper anonymous function, helper, to take care of the desired index offset.

With the following input:

str = {'x2 = -S1_2*(r1+a*K+a*P)+k*KS1_1+d*(PS1_1+KS1_2);'; ...
       'x3 = -S1_3*(r1+a*K+a*P)+k*KS1_2+d*(PS1_2+KS1_3);'; ...
       'x4 = -S1_4*(r1+a*K+a*P)+k*KS1_3+d*(PS1_3+KS1_4);'; ...
       'x5 = -S1_5*(r2+a*K+a*P)+k*KS1_4+d*(PS1_4+KS1_5);' ...
       };

We get the following output:

>> A = testcode(str)

A = 

    'x2 = -y(2)*(r1+a*K+a*P)+k*y(52)+d*(y(102)+y(53));'
    'x3 = -y(3)*(r1+a*K+a*P)+k*y(53)+d*(y(103)+y(54));'
    'x4 = -y(4)*(r1+a*K+a*P)+k*y(54)+d*(y(104)+y(55));'
    'x5 = -y(5)*(r2+a*K+a*P)+k*y(55)+d*(y(105)+y(56));'

Upvotes: 2

matlabgui
matlabgui

Reputation: 5672

At the very least you need to save the output from the regexprep command:

text1 = fileread('BaseJac3.txt');

for k = 1:4
  text1 = regexprep(text1,['PS1_' num2str(k)],['y(' num2str(k+101) ')']);
end
for k = 1:5
  text1 = regexprep(text1,['KS1_' num2str(k)],['y(' num2str(k+51) ')']);
end
for k = 2:5
  text1 = regexprep(text1,['S1_' num2str(k)],['y(' num2str(k) ')']);
end

Upvotes: 0

Related Questions