R help - Jun 2010 - Conditionally constructing columns in a data frame

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$existstr=="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)

...

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

I'm sure there's an easier way, but it's going to be easiest to get
a
useful response if we have a reproducible, minimal example, as the 
posting guide requests. ?tapply is probably involved.

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$existstr=="001",]
> 
>   read001$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)
> 
> ...
> 
> read2 <- rbind(read001, read011, read100, read110, read111)
> 
> 
> Isn't there an easier way to do this?
> 
> Thanks.
>

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
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT