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Re: Find part match in array

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Andrew Poulos wrote:

> If I have this
> 
> let arr1 = ["Today", "Freddy", "was", "here"];
> 
> what's a straightforward way to find that there's a match with this array
>    arr2 = ["Fred", "Yesterday"];
> (the first element "matches" the second element in arr1 ie 'Fred' is
> within 'Freddy')?
> 
> I started with
> const matched = arr1.some(a => arr2.includes(a));
> but I'm having trouble replacing the "includes" with a regexp and it to
> not error.

To arrive at a solution, it helps to think about the problem figuratively 
and to give your variables more meaningful names.  It also makes your code 
easier to understand later:

  let haystack = ["Today", "Freddy", "was", "here"];
  let needles = ["Fred", "Yesterday"];

  /* true if any of the needles was found in the haystack */
  const found = needles.some(needle => {
    /* Return true if the needle was found inside a straw of the haystack */
    return haystack.some(straw => (new RegExp(needle)).test(straw));
  });

Notice that there is a difference as to whether you match the contents of 
the second array against the contents of the first one or vice-versa.

Also notice that

  1. You do not have to use regular expressions.  Especially in ECMAScript
     Ed. 6 and newer, there are methods like String.prototype.includes()
     which with you can search for substrings easily.

  2. If you use regular expressions, the needle should be escaped if you
     want to search for a string verbatim instead of matching a pattern
     against an element:

       … new RegExp(needle.replace(/[\]\\^$*+?.(){}|[]/g, "\\$&")) …

     See also
     <https://github.com/PointedEars/JSX/blob/master/regexp.js#L1441> p.
 
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Find part match in array Andrew Poulos <ap_prog@hotmail.com> - 2020-08-17 10:56 +1000
  Re: Find part match in array Andrew Poulos <ap_prog@hotmail.com> - 2020-08-17 13:06 +1000
  Re: Find part match in array "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2020-08-16 20:54 -0700
  Re: Find part match in array JJ <jj4public@vfemail.net> - 2020-08-17 16:36 +0700
  Re: Find part match in array Julio Di Egidio <julio@diegidio.name> - 2020-08-17 05:01 -0700
  Re: Find part match in array Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2020-08-17 19:36 +0200
    Re: Find part match in array Andrew Poulos <ap_prog@hotmail.com> - 2020-08-18 09:02 +1000
      Re: Find part match in array Andrew Poulos <ap_prog@hotmail.com> - 2020-08-18 13:09 +1000
      Re: Find part match in array "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2020-08-18 11:28 +0200
        Re: Find part match in array "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2020-08-18 12:59 +0200
      Re: Find part match in array Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2020-08-18 21:59 +0200

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