Hi,
On Wednesday, February 15, 2012 08:02:44 AM Nerak wrote: > Hi all, > > I was wondering if there is a function kind of similar that splits a > dataframe, applies a function to each row and returns in a data frame. I > know ddply but this one isn’t useful in this situation. Why not? Sounds like a description of exactly the thing ddply is designed to do! > > I have a dataframe with values for each day (rows) for different objects > (columns). I have values for several years. Now, I want to do calculations > on only the data of that year. With the ddply function you can use as second > argument Year to split the data frame into years. But the function you use > is for that whole part so you get only one output value for that year (for > example the sum all the values in that column belonging to that year). Not true. ddply is designed to return a data.frame, not a single value. I think if you read the JSS article (http://www.jstatsoft.org/v40/i01) you'll find that ddply will do exactly what you want. Best, Ista I > want to calculate a new value for each day of that year (what would be > possible with apply if you have only data for one year). I found another > way to do this by using a for loop (y in Year[,]:Year[length(Year)] and > test2.dataframe<-test.dataframe[which(year==y)] to select the rows > belonging to that year on which I make to calculations. The problem is that > for loops take a lot of time to run and I’m trying to avoid using them > whenever possible. (Example almost reproducible script below) > > I’m also wondering if it’s possible to refer to a value of the row below > from another data vector or data frame or …. The line I mean in the script > below is this one (and is the one that is the course that the script doesn’t > work because that n is not known): > > test.number$numberb[y-Year[1]+1]<-length(which(test.starty==1 & > test.f[(n+1)]== 1 )) > > I want that for a certain row, the according value of test.starty (on the > row with the same number (e.g. n) ) = 1 and the according value of the row > below row n of test.f ==1. How can I do this without having to loop (which I > want to learn to avoid as much as possible). I tried to search on > Rhelpforum already and found: > http://r.789695.n4.nabble.com/How-to-calc-ratios-base-on-current-and-previou > s-row-td2341407.html My n+1 is based on the original value so there is > should be a solution without looping but I don’t understand how I should > index… > > I’ll illustrate what I mean with a loop to solve this kind (different > script) of problems: > test[1,]<-ifelse(AAA[1,]>1,1,0) > for (t in 2:10) > { > test <- ifelse(AAA[t,]>1 & AAA[t-1,]==0,1,0) > } > > > Below you can see how I did it with the for loop and what I want to create: > > > Year<-data.frame(Date=c(1980,1980,1980,1980,1981,1981,1981,1981,1982,1982,19 > 82,1982,1983,1983,1983,1983)) > test.b<-data.frame(C=c(0,0,0,0,5,2,0,0,0,15,12,10,6,0,0,0),B=c(0,0,0,0,9,6, > 2,0,0,24,20,16,2,0,0,0),F=c(0,0,0,0,6,5,1,0,0,18,16,12,10,5,1,0)) > test.start<-data.frame(C=c(0,0,0,0,1,0,0,0,0,1,0,0,0,0,0,0),B=c(0,0,0,0,1,0 > ,0,0,0,1,0,0,0,0,0,0),F=c(0,0,0,0,1,0,0,0,0,1,0,0,0,0,0,0)) > > > > test.2b<-test.b>1 > test.number<-data.frame(c(1980:1983)) > for (l in 1:nrow(test.b)) > { > for (y in 1980:1983) > { > > test.f<-test.2b[which(Year == y),l] > test.starty<-test.start[which(Year ==y),l] > test.number$numberb[y-Year[1]+1]<-length(which(test.starty==1 & > test.f[(n-1)]== 1 )) > > } > test.number[,l+1]<-cbind(test.number$numberb) > > } > > > If someone knows a way to get rid of the loops, let me know! Because I want > to make this script as fast as possible for larger datasets. I'm trying to > get through the apply family to find solutions but it's a hard issue. > > Many thanks in advance, > Kind regards, > Nerak > > -- > View this message in context: > http://r.789695.n4.nabble.com/function-similar-to-ddply-calculations-based- > on-previous-row-tp4390925p4390925.html Sent from the R help mailing list > archive at Nabble.com. > > ______________________________________________ > 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. ______________________________________________ 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.
