On Wed, Jul 1, 2009 at 9:39 AM, Duncan Murdoch<murd...@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@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.