[R] apply/return and reuse

[Gabor Grothendieck]

Here `out` is the same as the final value of `MyDF` in your code
using cumsum() instead of a loop:

set.seed(123)
DF <- data.frame(cbind(Event= 1:10, Initial=0,
   Offset=round(100*rnorm(10), 0), Final=0 ))
out <- transform(DF, Initial = 10000 + c(0, head(cumsum(DF$Offset), -1)))
out$Final <- with(DF, Initial + Offset)


On Sat, Jul 18, 2009 at 6:59 PM, Mark Knecht<markknecht at gmail.com> wrote:
> Hi,
>   No, it's not about cumsum specifically. It's about building up the
> list as the events go by.
>
>   I managed to create this code but it does depend on a for loop.
> Notice how the Final value on each row becomes the Initial value on
> the next row. Basically I want to build a data.frame with 5-10 values
> from the previous line which will help me determine what I would do on
> the current line.
>
>   This morning I had nothing while this afternoon I have this code.
> I'm not sure if a real R programmer like you would approve so I'm
> looking to get better.
>
> Thanks,
> Mark
>
>
> InitialValue = 10000
> MarginReq = 4000
>
> MyDF = data.frame(cbind(Event= 1:10, Initial=0,
>                        Offset=round(100*rnorm(10), 0) ,
>                        Final=0 ))
>
> MyDF$Initial[1] = InitialValue
> MyDF
>
> CurrentDate = 0
> CurrentFinal = InitialValue
> MyNumRows = dim(MyDF)[1]
> MyNumRows
>
> for (n in 1:MyNumRows) {
>   ## Save values from previous row
>   MyDF$Initial[n] = CurrentFinal
>
>   # Add Offset to current value to get new total
>
>   MyDF$Final[n] = MyDF$Initial[n] + MyDF$Offset[n]
>
>   ## Save values for next row
>   CurrentFinal = MyDF$Final[n]
> }
>
> MyDF
>
> On Sat, Jul 18, 2009 at 3:34 PM, Gabor
> Grothendieck<ggrothendieck at gmail.com> wrote:
>> I am not entirely clear on what you want to do but
>> if you simply want a cumulative sum use cumsum:
>>
>> cumsum(rep(100, 5)) + 10000
>>
>> or to do cumsum using Reduce and + try:
>>
>> Reduce("+", rep(100, 5), init = 10000, acc = TRUE)
>>
>> On Sat, Jul 18, 2009 at 3:59 PM, Mark Knecht<markknecht at gmail.com> wrote:
>>> Hi Gabor,
>>>   Thanks for the pointer to Reduce. It looks quite interesting. I
>>> made an attempt to use it but I'm not clear how I would move the
>>> output of the Reduce execution on row 1 to become the Initial value on
>>> Row 2. In this output:
>>>
>>>> MyDF
>>>   Event Initial Offset Final
>>> 1      1   10000    -31  9969
>>> 2      2       0     10    10
>>> 3      3       0   -133  -133
>>> 4      4       0    -91   -91
>>> 5      5       0   -145  -145
>>> 6      6       0     74    74
>>> 7      7       0      4     4
>>> 8      8       0     19    19
>>> 9      9       0   -120  -120
>>> 10    10       0     47    47
>>>>
>>>
>>> It seems that the intended use of Reduce is for when I have all the
>>> values previously set up in the array and then want to execute the
>>> same commands down through the array. That is very powerful and makes
>>> sense in most cases, but in my case I have to calculate the values on
>>> a line-by-line basis where the execution of Reduce on row 1 (the 9969)
>>> must become the Initial value on row 2 before Reduce it's work on row
>>> 2.
>>>
>>> I think I'm not fully grasping your intentions here.
>>>
>>> Code follows.
>>>
>>> Thanks,
>>> Mark
>>>
>>>
>>>
>>>
>>> InitialValue = 10000
>>>
>>> MyDF = data.frame(cbind(Event = 1:10, Initial = 0, Offset = 0 , Final = 0))
>>> MyDF$Offset = round(100*rnorm(10), 0)
>>> MyDF$Initial[1] = InitialCash
>>> MyDF
>>>
>>> AddPL = function(x) Reduce("+", x[2:3])
>>>
>>> MyDF$Final = AddPL(MyDF)
>>>
>>> MyDF
>>>
>>>
>>>
>>> On Fri, Jul 17, 2009 at 9:02 PM, Gabor
>>> Grothendieck<ggrothendieck at gmail.com> wrote:
>>>> See ?Reduce
>>>>
>>>> On Fri, Jul 17, 2009 at 11:10 PM, Mark Knecht<markknecht at gmail.com> wrote:
>>>>> Hi,
>>>>>   Is it possible to make something like the following code actually
>>>>> work? My goal in this example would be that I'd see results like
>>>>>
>>>>> 1   10000   10100
>>>>> 2   10100   10200
>>>>> 3   10200   10300
>>>>> 4   10300   10400
>>>>>
>>>>> In real usage the function would obviously do a lot more work, but the
>>>>> question I cannot answer myself yet is whether the apply can return a
>>>>> value from the work on one row and then use that value as the input to
>>>>> the function for the next row?
>>>>>
>>>>> Thanks,
>>>>> Mark
>>>>>
>>>>>
>>>>> ReturnLast = function (.row, NextInitial=100) {
>>>>>   .row$Initial = as.numeric(NextInitial)
>>>>>   .row$Final = as.numeric(.row$Initial+100)
>>>>> }
>>>>>
>>>>> MyStart = 10000
>>>>> X = data.frame(cbind(Event = 1:10, Initial = 0, Final = 0))
>>>>>
>>>>> X
>>>>>
>>>>> MyStart  = apply(X, 1, ReturnLast( X, MyStart))
>>>>>
>>>>> X
>>>>>
>>>>> ______________________________________________
>>>>> R-help at 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.
>>>>>
>>>>
>>>
>>
>