Using regexp to match multiple substrings, two questions

Hi all, Simple two part question.

1) I have a function where regexp needs to match two terms in a string.

st1='This string is going to be searched'

Expression should evaluate to True if st1 contains 'going' and 'search'.

I stole the following syntax from an old StackOverflow thread. I understand why it works. My question is, why is the '^' necessary? What is it doing?

hasMatch=~isempty(regexp(st1,'^(?=.*going).*(?=.*search).*'))

2) This code will be in a function. I would like to generalize it to any number of substrings that need to be matched. I understand varargin, but I'm not clever enough with regexp to code an arbitrary number of substrings that must be matched. Any help would be welcome.

Thanks!

-Aram

[Stephen23]

"Expression should evaluate to True if st1 contains 'going' and 'search'."

Question: Is the order significant? I.e. should the words only be matched if they are in exactly the order that you give them in?

[Aram Schiffman]

Right, good point. Answer is order-independent. I just need all N substrings to be matched -- somewhere.

Thanks, Aram

[Stephen23]

@Aram Schiffman: a regular expression is fundamentally order-dependent. You should consider other solutions.

Answer 1

[Stephen23]

You do not need to use regexp to fulfill the given requirements:

>> st1 = 'This string is going to be searched';
>> fun = @(s)~isempty(strfind(st1,s));
>> all(cellfun(fun,{'going','search'}))
ans = 1
>> all(cellfun(fun,{'going','elephant'}))
ans = 0

You can put this into a function, and provide as many inputs as you want:

function out = areinstr(str,varargin)
fun = @(s)~isempty(strfind(str,s));
out = all(cellfun(fun,varargin));
end

and tested:

>> areinstr(st1,'going','search','This')
ans = 1
>> areinstr(st1,'going','search','This','string')
ans = 1
>> areinstr(st1,'going','search','This','string','antelope')
ans = 0

[Aram Schiffman]

Thanks you! Very tidy solution. Also I didn't realize regular expressions were necessarily order-dependent. I thought there was a way for them not to be. Thanks for that crucial information, much appreciated.

Best, Aram

[Stephen23]

"I thought there was a way for them not to beI thought there was a way for them not to be"

There are some hacks that can be used to make them order-independent, but they make expression much more complex and slow.

Remember to accept the answer that best helps you to resolve your original question. That is the easiest way to show your thanks to the volunteers who helped you.

[Aram Schiffman]

Done. Thank you.