Need help with regexpi expression for multiple variants of the same phrase

I have a question regarding the use of regexpi to determine if certain string words are input into a text file. The text files were created by multiple individuals and use slightly different phrasing to mean the same variable. For example in a text file containing a gait evaluation the phrase 'slow cadence' was recorded, but 'slow cadence' can be denoted as 'slow cadence' or 'slow stepping'. My original code was as follows:

data=fileread('Test.txt');
A=isempty(regexpi(data{'slow cadence','slow stepping'}));

However, this version can return a false positive as it will mix and match string within the {}. For example the following code for the same file will return a '0' for the isempty function even though none of the string phrases match completely:

data=fileread('Test.txt');
A=isempty(regexpi(data{'fast cadence','slow stepping'}));

I feel like I am missing a simple command to indicate that A can be 'slow cadence' OR 'slow stepping'. Any help is much appreciated.

Answer 1

[Stephen23]

https://www.mathworks.com/help/matlab/matlab_prog/regular-expressions.html#f0-42884

You will probably find the 'ONCE' option also very very very useful (here I inverted the logical output, because true=contains is usually much simpler to work with than messing-with-your-head true=doesnotcontain):

str = fileread('Test.txt');
idx = ~isempty(regexpi(str, 'slow (cadence|stepping)','once'))

idx = logical
   1

Using regular expressions requires reading the documentation again and again and again and again and again... it takes quite a while to get profficient and comfortable using them. Also, make sure you read the documentation.

You might also find my interactive tool useful for helping to develop regular expressions:

https://www.mathworks.com/matlabcentral/fileexchange/48930-interactive-regular-expression-tool

I should also mention, that if you want to use regular expressions then you need to read the documentation. A lot.

PS: Another approach using the newer CONTAINS and patterns:

pat = regexpPattern('slow (cadence|stepping)');
idx = contains(str,pat, 'ignorecase',true)

idx = logical
   1

Answer 2

[Fifteen12]

I think you want to look at making regular expressions. Try this:

A=isempty(regexpi(data,'(slow cadence|slow stepping)'));

You'll probably want to do more case matching as well, using wild cards to subsitite for white spaace, etc. You can find more here