Re: finding the position of a pattern in list

• To: mathgroup at smc.vnet.net
• Subject: [mg64640] Re: [mg64583] finding the position of a pattern in list
• From: Pratik Desai <pdesai1 at umbc.edu>
• Date: Fri, 24 Feb 2006 00:19:47 -0500 (EST)
• References: <200602230534.AAA13180@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Gang Ma wrote:

>Hi,
>I am working on a program to do the following: My data is a list of 0
>and 1. For example, {0,0,1,1,1,0,0,1,1,1,0}. I want to find the
>positions of all the pattern of {0,1}.  In my previous example, the
>first {0,1} is at 2 and and the second {0,1} appears at 7. I can
>write a loop to do this, but I have several thousands such lists,
>the computation will be time consuming using loop.
>
>My question is whether it is possible to use the pattern match to do
>this quickly.  If not for the list, do I need to convert the list to
>strin
>
Here is what I tried using Reap and Sow, although it does not use any
pattern matching

Reap[Table[If[list1[[r]]-list1[[r+1]]===-1,Sow[r]],{r,1,Length[list1],1}]][[2]]//Flatten

In[1]:=

list1= {0,0,1,1,1,0,0,1,1,1,0}
Reap[Table[If[list1[[r]]-list1[[r+1]]===-1,Sow[r]],{r,1,Length[list1],1}]][[2]]//Flatten

Out[1]=
{0,0,1,1,1,0,0,1,1,1,0}

Out[2]=
{2,7}

Hope this helps

Pratik

```

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