[R] My code is too "loopy"

[Dimitri Liakhovitski]

Dennis, this is really great, thanks a lot!
Do you know how to prevent the result from omitting the first 2
values. I mean - it starts (within each group) with the 3rd row but
omits the first 2...
Dimitri

On Mon, Apr 25, 2011 at 5:31 PM, Dennis Murphy <djmuser at gmail.com> wrote:
> Hi:
>
> I think the embed() function is your friend here. From its help page example,
>
>> x <- 1:10
>> embed (x, 3)
>     [,1] [,2] [,3]
> [1,]    3    2    1
> [2,]    4    3    2
> [3,]    5    4    3
> [4,]    6    5    4
> [5,]    7    6    5
> [6,]    8    7    6
> [7,]    9    8    7
> [8,]   10    9    8
>
>
> Applying it to your test data,
>
> # h() creates a weighted average of the observations in each row
> h <- function(x) embed(x, 3) %*% c(0.5, 0.35, 0.15)
> library(plyr)
> ddply(mydata, "group", summarise, ma = h(myvalue))
>    group     ma
> 1  group1  11.00
> 2  group1  16.75
> 3  group1   9.25
> 4  group1   3.00
> 5  group1   0.00
> 6  group1   5.00
> 7  group2  85.00
> 8  group2  30.00
> 9  group2 150.00
> 10 group2 205.00
> 11 group2 115.00
> 12 group2  30.00
>
> Does that work for you? The rollapply() function in the zoo package
> may also be applicable with a similar input function that computes a
> weighted average.
>
> HTH,
> Dennis
>
>
> On Mon, Apr 25, 2011 at 1:50 PM, Dimitri Liakhovitski
> <dimitri.liakhovitski at gmail.com> wrote:
>> Hello!
>> I wrote a piece of code below that does the job but seems too "loopy" to me.
>> I was wondering if there is any way to make it more efficient/less "loopy"?
>> Thanks a lot for your hints!
>> Dimitri
>>
>> ### Creating example data set:
>>
>> mygroups<-c(rep("group1", 8),rep("group2", 8))
>> myweeks<-seq(as.Date("2010-01-04"), length = 8, by = "week")
>> values.w<-c(0,10,15,20,0,0,0,10,100,200,0,0,300,200,0,0)
>> mydata<-data.frame(group=mygroups,mydates=myweeks,myvalue=values.w)
>> mydata$group<-as.factor(mydata$group)
>> str(mydata)
>> (mydata)
>>
>> ### Doing the following within each level of the factor "mydata$group":
>> ### Create a new variable ("new.value") that equals:
>> ### myvalue in the same week * 0.5 +
>> ### myvalue 1 week ago  * 0.35
>> ### myvalue 2 weeks ago * 0.15
>>
>> groups<-levels(mydata$group)
>> (groups)
>>
>> mydata[["new.value"]]<-mydata[["myvalue"]]*0.5
>>
>> for(i in groups){   # looping through groups
>>  temp.data<-mydata[mydata$group %in% i,] # selecting values for one group
>>  temp.data[2,"new.value"]<-temp.data[["new.value"]][2]+temp.data[1,"myvalue"]*0.35
>> # 2nd new value
>>  for(myrow in 3:nrow(temp.data)){  # Starting in row 3 and looping through rows
>>    temp.data[myrow,"new.value"]<-temp.data[["new.value"]][myrow]+temp.data[(myrow-1),"myvalue"]*.35+temp.data[(myrow-2),"myvalue"]*.15
>>  }
>>  mydata[mydata$group %in% i,]<-temp.data
>> }
>>
>>
>> --
>> Dimitri Liakhovitski
>> Ninah Consulting
>> www.ninah.com
>>
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>> and provide commented, minimal, self-contained, reproducible code.
>>
>



-- 
Dimitri Liakhovitski
Ninah Consulting
www.ninah.com