[R] Adding collumn to existing data frame

[Ralf B]

Data frame is given by the rest of the script and not really an
option. Other than that, you are absolutely right.

Ralf

On Tue, Aug 3, 2010 at 11:34 PM, Dennis Murphy <djmuser at gmail.com> wrote:
> Wouldn't a list be a better object type if the variables you want to add
> have variable lengths? This way you don't have to worry about nuisances such
> as NA padding. Just a thought...
>
> Dennis
>
> On Tue, Aug 3, 2010 at 7:54 PM, Ralf B <ralf.bierig at gmail.com> wrote:
>>
>> Actually it does -- one has to use feed the result back into the
>> original variable:
>>
>> add.col <- function(df, vec, namevec){
>>        if (nrow(df) < length(vec) ){ df <-  # pads rows if needed
>>        rbind(df, matrix(NA, length(vec)-nrow(df), ncol(df),
>>                dimnames=list( NULL, names(df) ) ) )
>>        }
>>      length(vec) <- nrow(df) # pads with NA's
>>      df[, namevec] <- vec; # names new col properly
>>      return(df)
>> }
>>
>> mydata <- NULL
>> mydata <- data.frame(userid = c(5, 6, 5, 6, 5, 6), taskid = c(1, 1, 2, 2,
>> 3, 3),
>>      stuff = 11:16)
>> mydata  <- add.col(mydata, c(1,2,3,4),"test1")
>> mydata  <- add.col(mydata, c(1,2,3,4,5,6,7,8),"test2")
>> mydata
>>
>>
>> Thanks a lot, David and all others here you made the effort!
>> Ralf
>>
>>
>> On Tue, Aug 3, 2010 at 10:37 PM, David Winsemius <dwinsemius at comcast.net>
>> wrote:
>> >
>> > On Aug 3, 2010, at 10:35 PM, David Winsemius wrote:
>> >
>> >>
>> >> On Aug 3, 2010, at 8:32 PM, Ralf B wrote:
>> >>
>> >>> Hi experts,
>> >>>
>> >>> I am trying to write a very flexible method that allows me to add a
>> >>> new column to an existing data frame. This is what I have so far:
>> >>>
>> >>> add.column <- function(df, new.col, name) {
>> >>>        n.row <- dim(df)[1]
>> >>>        length(new.col) <- n.row
>> >>>        names(new.col) <- name
>> >>>        return(cbind(df, new.col))
>> >>> }
>> >>>
>> >>> df <- NULL
>> >>> df <- data.frame(a=c(1,2,3))
>> >>> df
>> >>> # corect: added NA to new collumn
>> >>> df <- add.column(df,c(1,2),'myNewColumn2')
>> >>> df
>> >>> # problem: not added, data frame should be extended with NAs
>> >>> add.column(df,c(1,2,3,4),'myNewColumn3')
>> >>> df
>> >>>
>> >>>
>> >>> However, there are two problems:
>> >>>
>> >>> 1) The column name is not renamed accurately but always set to
>> >>> 'new.col' . Surely this could be done outside the function, but it
>> >>> would be better if its self contained.
>> >>
>> >> Try this:
>> >>
>> >> add.col <- function(df, vec, namevec){
>> >>                         length(vec) <- nrow(df) # pads with NA's
>> >>                         cbind(df, namevec=vec)} # names new col
>> >> properly
>> >>
>> > Actually it doesn't name column correctky...  see below for a method
>> > with "[
>> > <-" .
>> >
>> >>> 2) It does not work for cases where new.col is longer than the length
>> >>> of the data frame. In such cases, I would like to add NA's to the data
>> >>> frame if it has less rows.
>> >>
>> >> Don't have a compact answer to this. (Tried re-dimensioning with "dim()
>> >> <-"  but it was not accepted by the interpreter.  Would need to add a
>> >> test
>> >> at the beginning and then pad with rows of NA's using rbind before
>> >> cbinding
>> >> as above.
>> >>
>> >> add.col <- function(df, vec, namevec){
>> >>              if (nrow(df) < length(vec) ){ df <-  # pads rows if needed
>> >>                    rbind(df, matrix(NA, length(vec)-nrow(df), ncol(df),
>> >>                                     dimnames=list( NULL, names(df) ) )
>> >> ) }
>> >>              length(vec) <- nrow(df) # pads with NA's
>> >>              df[, namevec] <- vec; # names new col properly
>> >>        return(df)}
>> >>
>> >>>
>> >>> Any ideas to to solve this?
>> >>
>> >> Has not been tested with columns of varying types.
>> >>
>> >
>> > David Winsemius, MD
>> > West Hartford, CT
>> >
>> >
>>
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>
>