Re: For Loop and Array related

*To*: mathgroup at smc.vnet.net*Subject*: [mg58001] Re: For Loop and Array related*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Thu, 16 Jun 2005 05:35:58 -0400 (EDT)*Organization*: The Open University, Milton Keynes, England*References*: <d8oucl$t6q$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

mchangun at gmail.com wrote: > Hi All, > > I have an array with 100 elements, all set to zero initially. Then I > want to randomly choose one element and increase its value by one, and > repeat this 16000 times. Here is my code: > > Lattice = Table[0, {n, 100}]; > For[i = 1, i = 16000, i++, Lattice[[Random[Integer, {1, 100}]]]++] > > So now if I add all the elements in the list Lattice together, I should > get 16000 (I use Total[Lattice] to get the sum of the list). But this > doesn't happen, and strangely, each time I run this, the sum of the > list is different! What am I doing wrong? > > Also I'm aware that a lot of Mathematica newbies try and write code > like it were C++ and I think i've fallen into this trap as well. So is > there a different (more Mathematica) way which I can implement the > above? > > Thanks in advanced. > Hi, Using the *Random* function directly within an assignment where the indices are supposed to be the same on both side might not be a good idea! You will find below the same function written in a slightly more Mathematica way: a *Do* loop is used since the index is not used in the body of the program and the index is first computed and saved in a variable before being used by the following instruction that increments the value of the corresponding element. Also, avoid defining symbol names that begin by a capital letter. In[1]:= data = Table[0, {n, 100}]; Do[index = Random[Integer, {1, 100}]; data[[index]]++, {16000}]; Total[data] Out[3]= 16000 Best regards, /J.M.