[R] Odp: calculations with vectors of unequal length

From: Petr PIKAL <petr.pikal_at_precheza.cz>
Date: Wed, 27 Apr 2011 14:04:59 +0200

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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