[R] Conditional operation on multiple columns from two data frames

[Peter Dalgaard]

tsippel wrote:
> The suggestion below was made.
> 
> df1$Date <- as.Date(df1$Date)
> df2$Date <- as.Date(df2$Date)
>  
> ifelse(df1$ID==df2$ID & df1$Date-df2$Date<0.5,df1$y-df2$y, NA)
> 
> However, because my dataframe rows do not align, I need the conditionals to
> be tested on every combination of cells.  I'm starting to think I need to
> use tapply?  
> 
> Tim  

I'd look at outer() or try a merge() before the operation to get things 
aligned. It is not clear to me what form of output you desire if you 
look at "every combination of cells".

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