I'm looking to search a String for a given value and then, if this value is found (anywhere in the string), I want to replace the entire string with a new one. Is this possible with regexprep?

As previously stated, I'm looking to search a string for a given value. If this value is present in the string, anywhere at all, I want to replace this entire string with an new one. I've spent about an hour trying to accomplish this with regexprep, but regexprep only seems to allow me to replace the portion of the string I'm searching for with a new string.

For example, I have a variable with a string value of the alphabet here:

String = abcde+fghijklm+nopq+rstuvwxyz

I want to search this string and make sure there aren't any random '+' signs in there to throw off my groove. If there are, I want to replace the entire string with the actual alphabet, without the random plus signs in there. I can search this string for a '+' using regexprep like this

 String= regexprep(String,'+','abcdefghijklmnopqrstuvwxyz')

but this method will replace only the plus sign with the alphabet, leaving me with an alphabet inside an alphabet. I want it to replace the entire incorret string with a the new, correct one. Is there any way to do this using regexprep? Or any other method?

My end goal is to search a string for a given value, and then, if found, replace the entire string with a new one. I appreciate any help.

[Azzi Abdelmalek]

Why an example without a '+' in it?

[Samuel]

Poor explanation of the problem on my part. Sorry about that, edited now.

Answer 1

[Walter Roberson]

regexprep(String, '.*\+.*', 'a':'z')

If there are no matches because there is no + then the replacement is not done, leaving everything intact.

[Samuel]

Thank you for you're help, you're solution is correct in the context of my example, but I don't think my original question was clear enough about what I'm actually trying to accomplish. I'll leave you the same reply I gave to Azzi, above, in an attempt to better explain myself.

 Thank you for your help! But I don't think its quite what I'm looking for. You answered my question in the sense that the solution you gave will remove the '+' signs leaving the original string intact. But I don't think I was clear enough in my original question as to what I'm looking to accomplish.

 In the real life issue I'm facing, which I tried (and seemingly failed) to simplify a bit in my question, requires that the string be replaced, rather than just removing the '+' signs entirely.

Let me try this again:

I'm writing a basic calculator application in Matlab for the experience and to learn a bit about the language as I do so. I have a string value which consists of user input which will be passed to a script later on. However, before I pass the user input to the script, I'm running a few checks on the string to make sure its formatted correctly. If its formatted incorrectly, I'm replacing the string with an error message for the user to read.

 So, for example, if the user were to input "3+++8" it would spit back an error because the user entered in multiple operators in a row. I'm using regexprep to search the string for multiple consecutive instances of either "+","-","*", or "/". I then replace the incorrectly formattted string with an error. But, with this method, and the example of "3+++8", the resulting string will be "3*error*8" because regexprep is simply replacing the consecutive plus signs it found with my error code. What I want it to do is either replace the string entirely, or simply delete everything that is not error in the string. Is there any way to do this? With regexprep or not?

 Hopefully this helps clarify things a bit. I tried to simplify my problem to make the question easier to ask, but I think that did more harm than good.

[Walter Roberson]

regexprep(String, '.*[-+*/][-+*/]+.*', 'error: multiple operators in a row')

However you need to consider your handling of negative numbers, as 3+-5 is usually considered to be (3)+(-5) which is valid if you have negative numbers.

If you wish the input string +5 to be valid as representing positive 5 then that means you are wanting to support "unary plus", in which case 3++8 would be parsed as (3)+(+8) which would be valid.

If you support negative numbers then any of your operators can be followed by - such as in 8/-2 . If you support unary plus as well then any of your operators can be followed by + such as in 8/+2 .

[Samuel]

Thank you for your help in solving my problem, and your addition advice on other possible cases where things might need to be different! I appreciate it.

Answer 2

[Azzi Abdelmalek]

What you want is to replace a '+' by a blank

String = 'abcdefghijklmnop+qrstuvwxyz'
String= regexprep(String,'+','')

or

String= strrep(String,'+','')

[Samuel]

Thank you for your help! But I don't think its quite what I'm looking for. You answered my question in the sense that the solution you gave will remove the '+' signs leaving the original string intact. But I don't think I was clear enough in my original question as to what I'm looking to accomplish.

In the real life issue I'm facing, which I tried (and seemingly failed) to simplify a bit in my question, requires that the string be replaced, rather than just removing the '+' signs entirely.

Let me try this again:

I'm writing a basic calculator application in Matlab for the experience and to learn a bit about the language as I do so. I have a string value which consists of user input which will be passed to a script later on. However, before I pass the user input to the script, I'm running a few checks on the string to make sure its formatted correctly. If its formatted incorrectly, I'm replacing the string with an error message for the user to read.

So, for example, if the user were to input "3+++8" it would spit back an error because the user entered in multiple operators in a row. I'm using regexprep to search the string for multiple consecutive instances of either "+","-","*", or "/". I then replace the incorrectly formattted string with an error. But, with this method, and the example of "3+++8", the resulting string will be "3*error*8" because regexprep is simply replacing the consecutive plus signs it found with my error code. What I want it to do is either replace the string entirely, or simply delete everything that is not error in the string. Is there any way to do this? With regexprep or not?

Hopefully this helps clarify things a bit. I tried to simplify my problem to make the question easier to ask, but I think that did more harm than good.

[Azzi Abdelmalek]

Samuel, please edit your original question, try to be brief and clear. You can illustrate with an example, post the expected result.