[R] Odp: calculations with vectors of unequal length

[Petr PIKAL]

Hi


r-help-bounces at r-project.org napsal dne 27.04.2011 13:30:13:

> Hi there,
> 
> this is probably simple but I can't seem to figure it out by myself...
> 
> I have two dataframes (df.1 and df.2):
> 
> df.1 <- data.frame(year=factor(rep(1:3,3)), level=rep(letters[1:3],3),
> number=c(11:19))
> df.2 <- data.frame(year=factor(c(1:5)), number=c(21:25))
> 
> I would like to create a new variable df.1$new, which is supposed to
> be the sum of each element of df.1$number and those elements of
> df.2$number, where df.2$year equals df.1$year.

merge(df.1,df.2, by.x="year", by.y="year", all.x=T)
  year level number.x number.y
1    1     a       11       21
2    1     a       17       21
3    1     a       14       21

than you can sum last 2 columns. I believe that sqldf package can do what 
you want more efficiently but I do not use it so I do not know exact 
syntax.

Regards
Petr


> 
> What would be the most efficient way of doing this?
> 
> Regards,
> EH
> 
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