[R] Oh apply functions, how you confuse me

[jim holtman]

Is this close to what you are asking for:

> require(data.table)
> Dt.. <- data.table(Df..)
> R <- Dt..[,
+     list(
+         sum = sum(Volume)
+         , weight = sum(Volume * Mph) / sum(Volume)
+         )
+     , by = list(Min5Break, Day, Hour, Dir)
+     ]
> R
   Min5Break Day Hour Dir      sum   weight
           1   1    0  NB 730.8880 32.60224
           2   1    0  NB 766.4083 35.88443
           3   1    0  SB 776.7592 32.66822
           4   1    0  SB 768.0923 33.55988
           5   1    0  NB 767.5472 36.00546
           6   1    0  NB 767.6600 30.38747
           7   1    0  SB 814.9662 31.88483
           8   1    0  SB 795.4855 30.91495
           9   1    0  NB 828.4439 31.57477
          10   1    0  NB 797.7522 29.49832
          11   1    0  SB 826.5165 32.74487
          12   1    0  SB 824.0942 36.28309
           1   2    1  NB 830.0683 29.59320
           2   2    1  NB 838.8179 34.59878
           3   2    1  SB 877.3518 30.77636
           4   2    1  SB 838.9765 30.90577
           5   2    1  NB 736.6560 30.54381
           6   2    1  NB 772.3622 31.40094
           7   2    1  SB 819.2347 29.22674
           8   2    1  SB 840.9048 32.59222
           9   2    1  NB 818.8383 37.55142
          10   2    1  NB 783.8896 32.54565
          11   2    1  SB 699.0401 30.76466
          12   2    1  SB 773.5594 35.87076
cn Min5Break Day Hour Dir      sum   weight
>


On Thu, Sep 1, 2011 at 1:11 PM, LCOG1 <jroll at lcog.org> wrote:
> Hi guys,
> I have a crap load of data to parse and have enjoyed creating a script that
> takes this data and creates a number of useful graphics for our area.  I am
> unable to figure out one summary though and its all cause I dont fully
> understand the apply family of functions.  Consider the following:
>
>
>
> #Create data
> Df..<-rbind(data.frame(Id=1:1008,Dir=rep(c("NB","NB","SB","SB"),252),Mph=runif(1008,0,65),
> Volume=runif(1008,0,19),Hour=rep(00,1008),Min5Break=rep(1:12,84),Day=rep(1,1008)),
> data.frame(Id=2009:2016,Dir=rep(c("NB","NB","SB","SB"),252),Mph=runif(1008,0,65),
> Volume=runif(1008,0,19),Hour=rep(01,1008),Min5Break=rep(1:12,84),Day=rep(2,1008)))
>
> #Example calc
> Results_<-list()
>
> #Sum Volume by 5 minute break by Day by Direction
> Results_$FiveMin.Direction<-tapply(Df..$Volume,list(Df..$Min5Break,Df..$Day,Df..$Hour,Df..$Dir),sum)
>
> The data is a snap shot of what im working with and I am trying to get to
> something similar to the last line where the volumes are summed.  What i
> want to do is to do a weighted average for the speed by 5 minute break.  So
> for all the speeds and volumes in a given hour of 5 minute break(12 per
> hour), i would want to
>
> sum(Volumes[1:12]*Speed[1:12]) / sum(Volumes[1:12]
>
> The output resembling the one from the above but having these weighted
> values.  I am assuming the sum function in the above would be replaced by a
> function doing the calculation but I am still not sure how to do this using
> apply functions, so perhaps this isnt the best option.
>
> Hope this is clear and hope you guys(and of course ladies) can offer some
> guidance.
>
> Cheers,
>  Josh
>
>
>
>
> --
> View this message in context: http://r.789695.n4.nabble.com/Oh-apply-functions-how-you-confuse-me-tp3784212p3784212.html
> Sent from the R help mailing list archive at Nabble.com.
>
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?