[R] apply/return and reuse

[Mark Knecht]

Very interesting. Thanks. Very concise! interesting use of cumsum.
I'll have to see if I can work that into my real code where I need to
take a conditional cumsum. I think it will work.

On my system the Final column doesn't seem quite right but that's OK.
There's enough here for me to study and I like that it doesn't have a
loop.

Thanks!



On Sat, Jul 18, 2009 at 5:10 PM, Gabor
Grothendieck<ggrothendieck at gmail.com> wrote:
> 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.
>>>>>>
>>>>>
>>>>
>>>
>>
>