[R] a difficult situation, how to do this using base function.

Jeff Newmiller
Sat, 22 Jul 2017 00:38:12 -0000

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If at all possible you should try to augment your table with an additional
table to contain the range.coordinates, or replace the range.coordinates
column with a list of tables. I have parsed your format into tables on the
fly, but this is inefficient and fragile.

######
DF <- data.frame( match.start=c( 5, 10, 100, 200 )
                 , range.coordinates = c( "1000-1050"
                                        , "1500-1555"
                                        , "5000-5050,6000-6180"
                                        , "100-150,200-260,600-900"
                                        )
                 , stringsAsFactors = FALSE
                 )
lookupFunction <- function( ms, rc ) {
   rcdf <- as.data.frame( lapply( as.data.frame( t( as.data.frame(
     strsplit( strsplit( rc, ",", fixed=TRUE )[[ 1 ]], "-" )
) ),
     stringsAsFactors=FALSE ), as.numeric ) )
   rcdf$V3 <- with( rcdf, cumsum( V2-V1 ) )
   rcq <- c( 0, rcdf$V3 )
   idx <- findInterval( ms, rcdf$V3 ) + 1
   rcdf$V1[ idx ] + ms - rcq[ idx ]
}

DF$match.start.updated <-
    unlist( lapply( seq.int( nrow( DF ) )
                  , function( i ) {
                       lookupFunction( DF$match.start[ i ]
                                     , DF$range.coordinates[ i ]
                                     )
                    }
                  )
         )
######

On Fri, 21 Jul 2017, Stephen HonKit Wong wrote:

> Hello,
>
> I have a following dataframe with many rows.
>
data.frame(match.start=c(5,10,100,200),range.coordinates=c("1000-1050","1500-1555","5000-5050,6000-6180","100-150,200-260,600-900"))
>
> match.start       range.coordinates
>           5               1000-1050
>          10               1500-1555
>         100               5000-5050,6000-6180
>         200              100-150,200-260,600-900
>
> I want to test for each row element in column "match.start" (e.g.
100 on
> 3rd row) if it is less than the accumulated range (e.g. for 5000-5050,
> 6000-6180, the accumulated range is: 50, 230), then update the match start
> as 6000+ (100-50) = 6050. The result is put on third column.
>
> match.start         range.coordinates   match.start.updated
>          5                   1000-1050                                 1005
>         10                 1500-1555                                  1510
>        100       5000-5050,6000-6180                         6050
>        200   100-150,200-260,600-900                        690
>
> Many thanks.
>
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>
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