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MathGroup Archive 2004

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Re: Programing operations with lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg50867] Re: [mg50856] Programing operations with lists
  • From: "Wolf, Hartmut" <Hartmut.Wolf at t-systems.com>
  • Date: Sat, 25 Sep 2004 01:55:05 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

>-----Original Message-----
>From: Guillermo Sanchez [mailto:guillerm at aida.usal.es]
To: mathgroup at smc.vnet.net
>Sent: Friday, September 24, 2004 10:42 AM
>To: mathgroup at smc.vnet.net
>Subject: [mg50867] [mg50856] Programing operations with lists
>
>
>Dear group,
> 
>I have two lists with this pattern
> 
>list1={{a1 , b1}, ..., {ai , bi}, ...};
> 
>list2={c1, ..., c(j-1),  cj, ...};
> 
>and a function f[x] (ie: f[x_] = 0.2 x);
> 
> 
>I would like grouping and sum the product bi f[ai] where
>C(j-1)<ai< cj
> 
> 
>I show it with an example:
> 
>list1 = {{0.71, 7378}, {1.6, 768}, {2, 2269}, {2.05, 0}, {2.35, 0},
>{2.4, 2608}, {2.6, 193}, {2.8, 4187}, {2.85, 204}, {2.95, 134}, 
>{3.2,776}, {3.25, 24}, {3.6, 6209}, {3.65, 0}, {3.7, 2809}, 
>{3.95, 1923}, 
>{4,2627}, {4.1, 25}, {4.15, 1}, {4.2, 0}, {4.25, -15}, {4.35, 1863}, 
>{4.4, 1797}, {4.45, 7533}, {4.5, 0}, {4.55, 53}, {4.7, 12045}, 
>{4.9, 7304},
>{4.95, 34}}; 
> 
> 
>list2 = {0.71, 3.2, 4, 4.5, 5}
> 
> 
>The solution should be:
> 
>{{7378 f[0.71] + .. +134 f[2.95]}, ... , {53 f[4.55]+...+34 f[4.95]}}
> 
>Thanks
> 
>Guillermo
>
>

Is it this what you want (from your example, not quite exactly what you specified)?

In[9]:=
(Plus @@ (#2 f[#1] &) @@@ Cases[list1, {x_, _} /; #1 <= x < #2] &) @@@ 
  Partition[list2, 2, 1]
Out[9]=
{7378 f[0.71] + 768 f[1.6] + 2269 f[2] + 2608 f[2.4] + 193 f[2.6] + 
    4187 f[2.8] + 204 f[2.85] + 134 f[2.95], 
 776 f[3.2] + 24 f[3.25] + 6209 f[3.6] + 2809 f[3.7] + 1923 f[3.95], 
 2627 f[4] + 25 f[4.1] + f[4.15] - 15 f[4.25] + 1863 f[4.35] + 1797 f[4.4] + 
    7533 f[4.45],
 53 f[4.55] + 12045 f[4.7] + 7304 f[4.9] + 34 f[4.95]}


I assume ordering of list2 as with your example.

--
Hartmut Wolf



P.S.: I tried an idea using Split, but only reached a near miss:

In[101]:= list0 = Transpose[list1][[1]]

In[119]:= i = 1; Split[list0, (If[# < list2[[i]], True, i++; False] &)]
Out[119]=
{{0.71}, {1.6, 2, 2.05, 2.35, 2.4, 2.6, 2.8, 2.85, 2.95, 3.2}, {3.25, 3.6, 
    3.65, 3.7, 3.95, 4}, {4.1, 4.15, 4.2, 4.25, 4.35, 4.4, 4.45, 4.5}, {4.55, 
    4.7, 4.9, 4.95}}

In[121]:= i = 5; Split[Reverse[list0], (If[# > list2[[i]], True, i--; False] &)]
Out[121]=
{{4.95}, {4.9, 4.7, 4.55, 4.5}, {4.45, 4.4, 4.35, 4.25, 4.2, 4.15, 4.1, 
    4}, {3.95, 3.7, 3.65, 3.6, 3.25, 3.2}, {2.95, 2.85, 2.8, 2.6, 2.4, 2.35, 
    2.05, 2, 1.6, 0.71}}


Can someone help me? (Split before, not after the fact; I mean to start a new grouping when test becomes false not endeng the preceeding)


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