[R] calculations with vectors of unequal length

[E Hofstadler]

Great, many thanks to Scott and Petr!



2011/4/27 Petr PIKAL <petr.pikal at precheza.cz>:
> 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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>
>