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Re: Finding the Position of Elements in a List that Contain a Substring

  • To: mathgroup at smc.vnet.net
  • Subject: [mg102218] Re: Finding the Position of Elements in a List that Contain a Substring
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Sat, 1 Aug 2009 04:03:13 -0400 (EDT)

On 7/31/09 at 5:53 AM, gregory.lypny at videotron.ca (Gregory Lypny)
wrote:

>Suppose I have a list of strings, say, sentences such as

>listOfStrings = {"The cat is here.", "It's not here.",  "Not in the
>catalogue,", "Where is the cat?"}

>and a string I want to search for

>searchString = "cat"

>I can use StringCases to pick off the elements that contain the
>search string

>StringCases[listOfStrings, __ ~~ searchString ~~ ___]

>{{"The cat is here."}, {}, {"Not in the catalogue,"}, {"Where is the
>cat?"}}

>But what if I just want to know the positions of the elements that
>are hits?  In this case, it's

>{1, 3, 4}

One way to do this would be:

In[1]:= searchString = "cat";
stringList = {{"The cat is here."}, {}, {"Not in the
catalogue,"}, \
{"Where is the
     cat?"}};

In[3]:= Position[
   StringPosition[#, searchString] /. {a_Integer, b_Integer} ->
1 & /@
    stringList, {1}][[All, 1]]

Out[3]= {1,3,4}

The idea here is using StringPosition returns a standard pattern
when there is a hit that can be made into any convenient value
using pattern matching. Now Position can be use to locate
instances of that value returning the desired positions of the hits.




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