[R] Conditionally constructing columns in a data frame

[David Winsemius]

On Jun 29, 2010, at 2:54 PM, Stuart Luppescu wrote:

> Hello, I have to construct 5 new columns in a data frame depending on
> the value of another of the columns in the data frame. The only way I
> could figure out to do this was to subset the data frame five times,  
> do
> the variable construction, and then rbind the subsets back together.
> Here's part of the code I used:
>
> read001 <- read[read$=="001",]
>
>  read001$era1end <- NA
>  read001$era2base <- NA
>  read001$era2end <- NA
>  read001$era3base <- read001$era1base
>  read001$era3end <- read001$era3base + (6 * read001$era3tr)
>
> read011 <- read[read$existstr=="011",]
>
>  read011$era1end <- NA
>  read011$era2base <- read011$era1base
>  read011$era2end <- read011$era2base + (4 * read011$era2tr)
>  read011$era3base <- read011$era2end
>  read011$era3end <- read011$era2end + (6 * read011$era3tr)
>
> ...

?split

processed_list <- split(read, read$existstr)
# then you have the dataframe in sections determined by existstr's value
# process within groups (but your example does not generalize in an  
obvious manner.)
# then:
final <- do.call(rbind , processed_list)

-- 
David.
>
> read2 <- rbind(read001, read011, read100, read110, read111)
>
>
> Isn't there an easier way to do this?
>
> Thanks.
>
> -- 
> Stuart Luppescu <slu at ccsr.uchicago.edu>
> University of Chicago
>
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David Winsemius, MD
West Hartford, CT