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Pattern problem: How to count from a long list of numbers all occurrences of 2 numbers next to each others?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87393] Pattern problem: How to count from a long list of numbers all occurrences of 2 numbers next to each others?
  • From: "Nasser Abbasi" <nma at 12000.org>
  • Date: Wed, 9 Apr 2008 05:56:39 -0400 (EDT)
  • Reply-to: "Nasser Abbasi" <nma at 12000.org>

Hello;

I think using Pattern is my weakest point in Mathematica.

I have this list, say this: (it is all a list of integers, no real numbers).

x = {1, 3, 3, 3, 2, 3, 3, 1, 3, 3}

And I want to count how many say a 3 followed immediately by 3. So in the 
above list, there will be 4 such occurrences. And if I want to count how 
many 1 followed by a 3, there will be 2 such cases, etc...

I tried Count[] but I do not know how to set the pattern for "3 followed by 
a comma followed by 3" or just "3 followed immediately by 3".

I tried few things, such as the following

In[68]:= Count[x, {3, 3}_]
Out[68]= 0

Also tried Cases, but again, I am not to good with Patterns, so not sure how 
to set this up at this moment.

Any ideas will be appreciated.

Nasser
I really need to sit down and study Patterns in Mathematica really well one 
day :) 



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