[R] ?max (so far...)

[Petr PIKAL]

Hi

what about do inside some function a subset of your whole data frame

fff <-  function( data, rows) {

data.1 <- data[1:rows,]

get all necessary stuf on data.1

return what you want

}

You can put a dimension check if you want the function to be more robust

Regards
Petr


r-help-bounces at r-project.org napsal dne 01.07.2009 19:26:17:

> On Wed, Jul 1, 2009 at 9:39 AM, Duncan Murdoch<murdoch at stats.uwo.ca> 
wrote:
> > On 01/07/2009 11:49 AM, Mark Knecht wrote:
> >>
> >> Hi,
> >>   I have a data.frame that is date ordered by row number - earliest
> >> date first and most current last. I want to create a couple of new
> >> columns that show the max and min values from other columns *so far* 
-
> >> not for the whole data.frame.
> >>
> >>   It seems this sort of question is really coming from my lack of
> >> understanding about how R intends me to limit myself to portions of a
> >> data.frame. I get the impression from the help files that the generic
> >> way is that if I'm on the 500th row of a 1000 row data.frame and want
> >> to limit the search max does to rows 1:500  I should use something
> >> like [1:row] but it's not working inside my function. The idea works
> >> outside the function, in the sense I can create tempt1[1:7] and the
> >> max function returns what I expect. How do I do this with row?
> >>
> >>   Simple example attached. hp should be 'highest p', ll should be
> >> 'lowest l'. I get an error message "Error in 1:row : NA/NaN argument"
> >>
> >> Thanks,
> >> Mark
> >>
> <SNIP>
> >>
> >> HighLow = function (MyFrame) {
> >>        temp1 <- MyFrame$p[1:row]
> >>        MyFrame$hp <- max(temp1) ## Highest p
> >>        temp1 <- MyFrame$l[1:row]
> >>        MyFrame$ll <- min(temp1) ## Lowest l
> >>
> >>        return(MyFrame)
> >> }
> >
> > You get an error in this function because you didn't define row, so R
> > assumes you mean the function in the base package, and 1:row doesn't 
make
> > sense.
> >
> > What you want for the "highest so far" is the cummax (for "cumulative
> > maximum") function.  See ?cummax.
> >
> > Duncan Murdoch
> >
> 
> Duncon,
>    OK, thanks. That makes sense, as long as I want the cummax from the
> beginning of the data.frame. (Which is exactly what I asked for!)
> 
>    How would I do this in the more general case if I was looking for
> the cummax of only the most recent 50 rows in my data.frame? What I'm
> trying to get down to is that as I fill in my data.frame I need to be
> able get a max or min or standard deviation of the previous so many
> rows of data - not the whole column - and I'm just not grasping how to
> do this. Is seems like I should be able to create a data set that's
> only a portion of a column while I'm in the function and then take the
> cummax on that, or use it as an input to a standard deviation, etc.?
> 
> Thanks,
> Mark
> 
> ______________________________________________
> 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.