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Re: Basic questions on list manipulation in the "Mathematica Way"

  • To: mathgroup at smc.vnet.net
  • Subject: [mg95577] Re: Basic questions on list manipulation in the "Mathematica Way"
  • From: dh <dh at metrohm.com>
  • Date: Thu, 22 Jan 2009 06:58:25 -0500 (EST)
  • References: <gl71s8$c41$1@smc.vnet.net>


Hi,

I would store the data in a function. Further, I would not store 

attribute names more than once. Here is an example:

person[John]={1,2,3}

this declares a person "John" with attribute values: 1,2,3

To pick a certain attribute:

person[name_,attr1]:= person[name][[1]];

person[name_,attr2]:= person[name][[2]];

person[name_,attr3]:= person[name][[2]];

This scheme can be extended.

hope this helps, Daniel





dangerrity at gmail.com wrote:

> Hello,

> 

> I have some basic questions about using lists in Mathematica.

> Specifically I have a table that serves as sort of a database with the

> following structure:

> 

> ct = {

>           { sym1 -> {val1->20, val2->300, val3->1000, ... },

>           { sym2 -> {val1->50, val2->500, val3->20000,...},

>           ...

>        }

> 

> sym1, sym2, ... are people and val1, val2 ... represent attributes of

> each person.

> 

> Now I'm trying to go in and modify values.  I can do it, but I think

> not well and I think with a "programming language" mindset instead of

> a "Mathematica mindset."

> 

> Here is my specific question.  In order to change a specific value in

> the list above (valxxx) for a given individual (symxxx), I created

> this function:

> 

> changeVal[ who_, class_, amnt_ ] := (

>     ct[[ Position[ ct, who ][[ 1, 1 ]], 2 ]] =

>     ReplacePart[ ct[[ Position[ ct, who ][[ 1, 1 ]], 2 ]],

>      Position[ ct[[ Position[ ct, who ][[ 1, 1 ]] ]], class ][[ 1,

> 2 ]] -> (class -> amnt) ]

> );

> 

> Now I know there is a better way than that using list manipulation and

> patterns.  Can some of you experienced pros help me out?  I call this

> "write only" code because I don't know that I could explain it once

> it's written.

> 

> Perhaps a more fundamental question: is this the right way to store

> data in lists?  Or would it be better to just have the values and

> reference them by index number?

> 

> Thanks for your patience with a simple question.

> 

> 




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