[R] apply/return and reuse

[Mark Knecht]

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.
>>
>