Re: Means

*To*: mathgroup at smc.vnet.net*Subject*: [mg73924] Re: Means*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Sat, 3 Mar 2007 01:04:14 -0500 (EST)*Organization*: The Open University, Milton Keynes, UK*References*: <es9295$3na$1@smc.vnet.net>

JGBoone at gmail.com wrote: > I was wondering if anyone knew how to take the mean of only half of a > paired order. I have a table of 3000 pairs and want to take the > average of the last half of the last number in the pair. I do this by > N[Mean[Map[Last, list]]] is there any way to map to the last half of > the list. Thanks You could use Take with a negative second argument as in the following: In[1]:= list = Table[{Random[], Random[Integer, 10]}, {20}] Out[1]= {{0.134179, 2}, {0.122422, 8}, {0.540121, 5}, {0.490495, 7}, {0.97891, 4}, {0.458892, 4}, {0.698429, 1}, {0.549347, 6}, {0.214567, 9}, {0.670112, 10}, {0.118525, 2}, {0.754165, 7}, {0.2386, 6}, {0.233337, 1}, {0.838034, 7}, {0.126505, 9}, {0.597379, 8}, {0.469553, 1}, {0.405691, 3}, {0.845892, 0}} In[2]:= N[Mean[Last /@ Take[list, -10]]] Out[2]= 4.4 In[3]:= N[Mean[Last /@ Take[list, -Length[list]/2]]] Out[3]= 4.4 Regards, Jean-Marc