[R] Fastest way to compare a single value with all values in one column of a data frame
Jessica Streicher
j.streicher at micromata.de
Wed Jan 30 13:38:44 CET 2013
If you wanted this for all values in x that are smaller, i'd use
x[x$a < y$a,] <- y
for just the smallest:
x[intersect(which(x$a < y$a),which.min(x$a)),] <- y
On 29.01.2013, at 22:11, Dimitri Liakhovitski wrote:
> Hello!
>
> I have a large data frame x:
> x<-data.frame(item=letters[1:5],a=1:5,b=11:15) # in actuality, x has 1000
> rows
> x$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]]
>
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