Replacing Text with Error Message if Text not Found in Matlab - matlab

Question

I have a function that replaces a piece of text, and it became relevant that this function needs to issue an error in case it fails to do so.
One way to do so would be:
text_var = 'The whole big text';
if(~contains(text_var,'The part that will be replaced')))
throw(MException('MF:error','The part to be replaced is not in the text!'))
else
text_var = strrep(text_var,'The part that will be replaced','The replacement');
end
However, this seems not to be efficient. I can assume the text, if it appears does so only once. But I'd like to make a single call to a function operating on text_var. Is there no text replacement function in Matlab that returns an error if the replacement failed?

Answer 1

You could do the replace, and just check if the new string's length is unchanged (this assumes the original and replacement strings are different lengths)
text_var = 'the whole big text';
n = numel( text_var );
text_var = strrep( text_var, 'replace me', 'with this' );
if numel( text_var ) == n
error( 'No replacements made' );
end
If you can't make that assumption, you could use strfind to get the indices of the string. This will be empty if not found (so error), or you can use it to manually remove the string. Especially easy as you state it will appear at most once.
text_var = 'the whole big text';
removeStr = 'replace this';
k = strfind( text_var, removeStr );
if isempty( k )
error( 'No replacements made' );
end
text_var( k:k+numel(removeStr)-1 ) = []; % Remove string
Because you're only matching once, you might find that regexp is quicker than strfind, as you can use the 'once' argument of regexp to make it stop on the first match
k = regexp( text_var, removeStr, 'once' ); % instead of using strfind