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MathGroup Archive 2009

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Working with Lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg104327] Working with Lists
  • From: BenT <brtubb at pdmusic.org>
  • Date: Wed, 28 Oct 2009 04:05:19 -0500 (EST)

I have several practical problems which I need to solve, and
understand, preferable in a generic matter well, before needing to
apply them specifically pertaining to:

using a "generic" example:

f={{1,2,},{3,4,},{5,6},{7,8}}

NOTE: the use of 1 thru 8 for the values is purely arbitrary so please
to do not apply any "simplifications" based on their present values.

I know have to obtain the sum of all of the elements in each of the
lists by using

Apply[Plus,f]

and from it, I can use the Part function or "[[]]" method of obtaining
each result as needed.

asum=Apply[Plus,f][[1]]
bsum=Apply[Plus,f][[2]]

What I further need are methods to:

(1) obtain separate lists, call them a and b which contain just the
1st and 2nd elements of each sublist respectively

(2) then after further, if eny modification of either list's data (a
copletely separate issue), I need to know the method of how to merge
them, and replace the original data.

I know how to apply Rule's to transform data on a list of single
elements, but not for "larger" lists.

Consider this code:

f={{0,1},{7,1},{12,2}}

rd={1->1/4,2=1/2}

How can I apply the rd "rule" (or any Rule) to just the second
elements' 2nd values in the f list? And more importantly how are such
things done generically?

And someone please define distinct differences between:

(1) list
(2) sequence
(2) vector
(2) array
(3) matrix/table

I'm using Mathemata Version 7, but am only a "hobbies" at it. Music is
my primary interest.

--- Benjamin Tubb


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