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.