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MathGroup Archive 2007

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Re: Using Part

  • To: mathgroup at smc.vnet.net
  • Subject: [mg77094] Re: [mg77057] Using Part
  • From: DrMajorBob <drmajorbob at bigfoot.com>
  • Date: Sun, 3 Jun 2007 06:12:42 -0400 (EDT)
  • References: <18064701.1180782141199.JavaMail.root@m35>
  • Reply-to: drmajorbob at bigfoot.com

Select operates on one top-level element at a time, so #2 is undefined. 
 
Try Split, instead.

data = {{16871, I7, 614, 48876, 850, {2006, 12, 2}}, {16871, I7,
     538.3, 49803, 850, {2007, 1, 8}}, {16871, I7, 474.8, 50655,
     850, {2007, 2, 1}}, {16871, I7, 428.1, 51430,
     850, {2007, 2, 20}}, {16871, I7, 74.9, 51430,
     850, {2007, 2, 20}}, {16871, I7, 535, 52348,
     850, {2007, 3, 20}}, {16871, I7, 395.9, 53383,
     850, {2007, 5, 9}}};
split = Split[SortBy[data, Last], Last[#1] == Last[#2] &];
sums = Total[#[[All, 3]]] & /@ %;
result = First /@ split;
result[[All, 3]] = sums;
result

{{16871, I7, 614, 48876, 850, {2006, 12, 2}}, {16871, I7, 538.3,
   49803, 850, {2007, 1, 8}}, {16871, I7, 474.8, 50655,
   850, {2007, 2, 1}}, {16871, I7, 503., 51430,
   850, {2007, 2, 20}}, {16871, I7, 535, 52348,
   850, {2007, 3, 20}}, {16871, I7, 395.9, 53383, 850, {2007, 5, 9}}}

SortBy is unnecessary if the list is already sorted.

I could have used #1[[6]]==#2[[6]]& as the Split criterion, but I liked  

Last a bit better.

Bobby

On Sat, 02 Jun 2007 03:15:18 -0500, Clifford Martin <camartin at snet.net> 

wrote:

>   Group,
>
> I need some educational help. Below is a list of lists I'm trying to  
> manipulate. Notice that the date is in the 6th place in each list.  What  
> I want to do is 1) identify the lists with identical dates and 2) once 
> I've done that add the third element of each list with identical dates 
> together and 3) eliminate the two original lists.
>
> {{{16871,I7,614,48876,850,{2006,12,2}},{16871,I7,538.3,49803,850,{2007,1,8}},
> {16871,I7,474.8,50655,850,{2007,2,1}},{16871,I7,428.1,51430,850,{2007,2,20}},
> {16871,I7,74.9,51430,850,{2007,2,20}},{16871,I7,535,52348,850,{2007,3,20}},
> {16871,I7,395.9,53383,850,{2007,5,9}}}
>
> So what I would end up with would be:
>
> {{{16871,I7,614,48876,850,{2006,12,2}},{16871,I7,538.3,49803,850,{2007,1,8}},
>  {16871,I7,474.8,50655,850,{2007,2,1}},{16871,I7,503,51430,850,{2007,2,20}},
>   {16871,I7,535,52348,850,{2007,3,20}},{16871,I7,395.9,53383,850,{2007,5,9}}}
> There is something about using Part that I'm not understanding. In the
> list below if I say:
>  Part[list,4,6]==Part[list,5,6] I get
>  True
> but if I try to find it with an anonymous function like
>  Select[list,Part[#1,6]==Part[#2,6] this doesn't find it. Clearly I'm  
> not understanding how to use these functions with Part. I've tried many  
> variations of this and it just shows I'm not understanding something  
> fundamental.
>  Thanks for your help in advance.
>
> Cliff
>
>



-- 

DrMajorBob at bigfoot.com


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