Hi Dimitri,
Does this help?
k1<-data.frame(item=sample(rep(letters),10,replace=T),a=c(1:10),b=11:20)
k2<-data.frame(item="f",a=3,b=10)
merge<-function(y,x)
{
if(y$a>min(x$a))
{
x<-rbind(x,y)
x<-x[-which.min(x$a),]
}
return(x)
}
merge(k2,k1)
or much faster way would be to refer "library(sqldf)".
--- On Wed, 30/1/13, Dimitri Liakhovitski <dimitri.liakhovit...@gmail.com>
wrote:
From: Dimitri Liakhovitski <dimitri.liakhovit...@gmail.com>
Subject: [R] Fastest way to compare a single value with all values in one
column of a data frame
To: "r-help" <r-help@r-project.org>
Date: Wednesday, 30 January, 2013, 2:41 AM
Hello!
I have a large data frame x:
x<-data.frame(item=letters[1:5],a=1:5,b=11:15) # in actuality, x has 1000
rows
x$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/>
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