Re: Pattern Matching in Lists

*To*: mathgroup at smc.vnet.net*Subject*: [mg35596] Re: Pattern Matching in Lists*From*: "Allan Hayes" <hay at haystack.demon.co.uk>*Date*: Mon, 22 Jul 2002 02:10:51 -0400 (EDT)*References*: <ahdfd2$i3i$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Carl, Pushing your idea a bit further and avoiding one Drop and a subtraction of lists: w=Table[Random[Integer],{1000000}]; Tr[Drop[w,-1](Drop[w,-1]-Drop[w,1])]//Timing {7.85 Second,249850} (Tr[#]-Tr[# Drop[w,1]])&[Drop[w,-1] ]//Timing {2.75 Second,249850} -- Allan --------------------- Allan Hayes Mathematica Training and Consulting Leicester UK www.haystack.demon.co.uk hay at haystack.demon.co.uk Voice: +44 (0)116 271 4198 Fax: +44 (0)870 164 0565 "Carl K. Woll" <carlw at u.washington.edu> wrote in message news:ahdfd2$i3i$1 at smc.vnet.net... > Anthony and newsgroup, > > I thought of another method of solving this problem which is 5 or 6 times > faster than my previous version. Here is a test case. > > tst=Table[Random[Integer],{1000000}]; > > My first solution was > > In[16]:= > Count[Partition[tst,2,1],{1,0}]//Timing > Out[16]= > {0.704 Second, 249722} > > My second solution is > > In[17]:= > Tr[Drop[tst,-1](Drop[tst,-1]-Drop[tst,1])]//Timing > Out[17]= > {0.125 Second, 249722} > > Carl Woll > Physics Dept > U of Washington > > "Anthony Mendes" <amendes at zeno.ucsd.edu> wrote in message > news:ah5qce$59o$1 at smc.vnet.net... > >Hello, > > > > Suppose w={1,1,1,0,0,1,0,1,0,0,1,0,0}. > > > > How can I count the number of occurrences of a 1 in w immediately > > followed by a 0 in w? > > > > I have tried every incarnation of Count[] I can think of; for example, > > > > Count[w,{___,1,0,___}] > > > > does not seem to work. In general, how can I count the number of > > occurrences of a 1 followed by a 0 in a list of 1's and 0's? Thank you! > > > > > > -- > > Tony > > _____________________ > > amendes at math.ucsd.edu > > > > > > > > > > >