Sorry about the lack of code, but using Davids example, would:
tapply(itemPrice, INDEX=orderID, FUN=sum)
work?
-Ken Hutchison
On Aug 3, 2554 BE, at 2:09 PM, David Winsemius <dwinsem...@comcast.net> wrote:
>
> On Aug 3, 2011, at 2:01 PM, Ken wrote:
>
>> Hello,
>> Perhaps transpose the table attach(as.data.frame(t(data))) and use ColSums()
>> function with order id as header.
>> -Ken Hutchison
>
> Got any code? The OP offered a reproducible example, after all.
>
> --
> David.
>>
>> On Aug 3, 2554 BE, at 1:12 PM, David Winsemius <dwinsem...@comcast.net>
>> wrote:
>>
>>>
>>> On Aug 3, 2011, at 12:20 PM, jim holtman wrote:
>>>
>>>> This takes about 2 secs for 1M rows:
>>>>
>>>>> n <- 1000000
>>>>> exampledata <- data.frame(orderID = sample(floor(n / 5), n, replace =
>>>>> TRUE), itemPrice = rpois(n, 10))
>>>>> require(data.table)
>>>>> # convert to data.table
>>>>> ed.dt <- data.table(exampledata)
>>>>> system.time(result <- ed.dt[
>>>> + , list(total = sum(itemPrice))
>>>> + , by = orderID
>>>> + ]
>>>> + )
>>>> user system elapsed
>>>> 1.30 0.05 1.34
>>>
>>> Interesting. Impressive. And I noted that the OP wanted what cumsum would
>>> provide and for some reason creating that longer result is even faster on
>>> my machine than the shorter result using sum.
>>>
>>> --
>>> David.
>>>>>
>>>>> str(result)
>>>> Classes ‘data.table’ and 'data.frame': 198708 obs. of 2 variables:
>>>> $ orderID: int 1 2 3 4 5 6 8 9 10 11 ...
>>>> $ total : num 49 37 72 92 50 76 34 22 65 39 ...
>>>>> head(result)
>>>> orderID total
>>>> [1,] 1 49
>>>> [2,] 2 37
>>>> [3,] 3 72
>>>> [4,] 4 92
>>>> [5,] 5 50
>>>> [6,] 6 76
>>>>>
>>>>
>>>>
>>>> On Wed, Aug 3, 2011 at 9:25 AM, Caroline Faisst
>>>> <caroline.fai...@gmail.com> wrote:
>>>>> Hello there,
>>>>>
>>>>>
>>>>> I’m computing the total value of an order from the price of the order
>>>>> items
>>>>> using a “for” loop and the “ifelse” function. I do this on a large
>>>>> dataframe
>>>>> (close to 1m lines). The computation of this function is painfully slow:
>>>>> in
>>>>> 1min only about 90 rows are calculated.
>>>>>
>>>>>
>>>>> The computation time taken for a given number of rows increases with the
>>>>> size of the dataset, see the example with my function below:
>>>>>
>>>>>
>>>>> # small dataset: function performs well
>>>>>
>>>>> exampledata<-data.frame(orderID=c(1,1,1,2,2,3,3,3,4),itemPrice=c(10,17,9,12,25,10,1,9,7))
>>>>>
>>>>> exampledata[1,"orderAmount"]<-exampledata[1,"itemPrice"]
>>>>>
>>>>> system.time(for (i in 2:length(exampledata[,1]))
>>>>> {exampledata[i,"orderAmount"]<-ifelse(exampledata[i,"orderID"]==exampledata[i-1,"orderID"],exampledata[i-1,"orderAmount"]+exampledata[i,"itemPrice"],exampledata[i,"itemPrice"])})
>>>>>
>>>>>
>>>>> # large dataset: the very same computational task takes much longer
>>>>>
>>>>> exampledata2<-data.frame(orderID=c(1,1,1,2,2,3,3,3,4,5:2000000),itemPrice=c(10,17,9,12,25,10,1,9,7,25:2000020))
>>>>>
>>>>> exampledata2[1,"orderAmount"]<-exampledata2[1,"itemPrice"]
>>>>>
>>>>> system.time(for (i in 2:9)
>>>>> {exampledata2[i,"orderAmount"]<-ifelse(exampledata2[i,"orderID"]==exampledata2[i-1,"orderID"],exampledata2[i-1,"orderAmount"]+exampledata2[i,"itemPrice"],exampledata2[i,"itemPrice"])})
>>>>>
>>>>>
>>>>>
>>>>> Does someone know a way to increase the speed?
>>>>>
>>>>>
>>>>> Thank you very much!
>>>>>
>>>>> Caroline
>>>>>
>>>>> [[alternative HTML version deleted]]
>>>>>
>>>>>
>>>>> ______________________________________________
>>>>> R-help@r-project.org mailing list
>>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>>> 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?
>>>>
>>>> ______________________________________________
>>>> R-help@r-project.org mailing list
>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide
>>>> http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>> David Winsemius, MD
>>> West Hartford, CT
>>>
>>> ______________________________________________
>>> R-help@r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius, MD
> West Hartford, CT
>
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