[R] Fastest way to compare a single value with all values in one column of a data frame
arun
smartpink111 at yahoo.com
Wed Jan 30 15:22:14 CET 2013
Hi,
I guess you could also use:
x[match(min(x$a),x$a[x$a<y$a]),]<- y
x
# item a b
#1 f 3 10
#2 b 2 12
#3 c 3 13
#4 d 4 14
#5 e 5 15
A.K.
----- Original Message -----
From: Dimitri Liakhovitski <dimitri.liakhovitski at gmail.com>
To: r-help <r-help at r-project.org>
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/>
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