Thank you, everyone! I'll try to test those different approaches. Really appreciate your help! Dimitri
On Wed, Jan 30, 2013 at 11:03 AM, arun <[email protected]> wrote: > HI, > > Sorry, my previous solution doesn't work. > This should work for your dataset: > set.seed(1851) > x<- > data.frame(item=sample(letters[1:5],20,replace=TRUE),a=sample(1:15,20,replace=TRUE),b=sample(20:30,20,replace=TRUE),stringsAsFactors=F) > y<- data.frame(item="f",a=3,b=10,stringsAsFactors=F) > x[x$a%in%which.min(x[x$a<y$a,]$a),]<- y #if there are multiple minimum > values > > set.seed(1241) > x1<- > data.frame(item=sample(letters[1:10],1e4,replace=TRUE),a=sample(1:30,1e4,replace=TRUE),b=sample(1:100,1e4,replace=TRUE),stringsAsFactors=F) > y1<- data.frame(item="f",a=3,b=10,stringsAsFactors=F) > length(x1$a[x1$a==1]) > #[1] 330 > system.time({x1[x1$a%in%which.min(x1[x1$a<y1$a,]$a),]<- y1}) > # user system elapsed > # 0.000 0.000 0.001 > length(x1$a[x1$a==1]) > #[1] 0 > > > #For some reason, it is not working when the multiple number of minimum > values > some value > > set.seed(1241) > x1<- > data.frame(item=sample(letters[1:10],1e5,replace=TRUE),a=sample(1:30,1e5,replace=TRUE),b=sample(1:100,1e5,replace=TRUE),stringsAsFactors=F) > y1<- data.frame(item="f",a=3,b=10,stringsAsFactors=F) > length(x1$a[x1$a==1]) > #[1] 3404 > x1[x1$a%in%which.min(x1[x1$a<y1$a,]$a),]<- y1 > length(x1$a[x1$a==1]) > #[1] 3404 #not getting replaced > > #However, if I try: > set.seed(1241) > x1<- > data.frame(item=sample(letters[1:10],1e6,replace=TRUE),a=sample(1:5000,1e6,replace=TRUE),b=sample(1:100,1e6,replace=TRUE),stringsAsFactors=F) > y1<- data.frame(item="f",a=3,b=10,stringsAsFactors=F) > length(x1$a[x1$a==1]) > #[1] 208 > system.time(x1[x1$a%in%which.min(x1[x1$a<y1$a,]$a),]<- y1) > #user system elapsed > # 0.124 0.016 0.138 > length(x1$a[x1$a==1]) > #[1] 0 > > > #Tried Jessica's solution: > set.seed(1851) > x<- > data.frame(item=sample(letters[1:5],20,replace=TRUE),a=sample(1:15,20,replace=TRUE),b=sample(20:30,20,replace=TRUE),stringsAsFactors=F) > y<- data.frame(item="f",a=3,b=10,stringsAsFactors=F) > x[intersect(which(x$a < y$a),which.min(x$a)),] <- y > x > # item a b > #1 a 8 25 > #2 a 10 26 > #3 f 3 10 #replaced > #4 e 15 26 > #5 b 13 20 > #6 a 5 23 > #7 d 4 29 > #8 e 2 24 > #9 c 7 30 > #10 e 14 24 > #11 d 2 20 > #12 e 10 21 > #13 c 13 27 > #14 d 12 23 > #15 b 11 26 > #16 e 5 22 > #17 c 1 26 #it is not replaced > #18 a 8 21 > #19 e 10 26 > #20 c 2 22 > > > > A.K. > > > > > > ----- Original Message ----- > From: Dimitri Liakhovitski <[email protected]> > To: r-help <[email protected]> > Cc: > Sent: Tuesday, January 29, 2013 4:11 PM > Subject: [R] Fastest way to compare a single value with all values in one > column of a data frame > > Hello! > > I have a large data frame x: > x<-data.frame(item=letters[1:5],a=1:5,b=11:15) # in actuality, x has 1000 > rows > x$item<-as.character(x$item) > I also have a small data frame y with just 1 row: > y<-data.frame(item="f",a=3,b=10) > y$item<-as.character(y$item) > > I have to decide if y$a is larger than the smallest of all the values in > x$a. If it is, I want y to replace the whole row in x that has the lowest > value in column a. > This is how I'd do it. > > if(y$a>min(x$a)){ > whichmin<-which(x$a==min(x$a)) > x[whichmin,]<-y[1,] > } > > > I am wondering if there is a faster way of doing it. What would be the > fastest possible way? I'd have to do it, unfortunately, many-many times. > > Thank you very much! > > -- > Dimitri Liakhovitski > gfk.com <http://marketfusionanalytics.com/> > > [[alternative HTML version deleted]] > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html> > and provide commented, minimal, self-contained, reproducible code. > > -- Dimitri Liakhovitski gfk.com <http://marketfusionanalytics.com/> [[alternative HTML version deleted]] ______________________________________________ [email protected] 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.
