[R] Adding a column to an **empty** data.frame

[Emmanuel Levy]

Dear Bill,

Thanks a lot this is what I was looking for.

Emmanuel

On 2 November 2016 at 15:59, William Dunlap <wdunlap at tibco.com> wrote:

> Give your new column a vector type - NULL cannot be extended beyond length
> 0.  Also, the syntax df$col<-NULL means to remove 'col' from 'df'.
>
> > df <- data.frame(id=integer(0), data=numeric(0))
> > df$new.col <- character(0)
> > str(df)
> 'data.frame':   0 obs. of  3 variables:
>  $ id     : int
>  $ data   : num
>  $ new.col: chr
>
> (Think of 'zero-row' or 'zero-column' data.frames, not 'empty'
> data.frames, which could be either.)
>
>
>
> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com
>
> On Wed, Nov 2, 2016 at 6:48 AM, Emmanuel Levy <emmanuel.levy at gmail.com>
> wrote:
>
>> Dear All,
>>
>> This sounds simple but can't figure out a good way to do it.
>>
>> Let's say that I have an empty data frame "df":
>>
>> ## creates the df
>> df = data.frame( id=1, data=2)
>>
>> ## empties the df, perhaps there is a more elegant way to create an empty
>> df?
>> df = df[-c(1),]
>>
>> > df
>> [1] id   data
>> <0 rows> (or 0-length row.names)
>>
>> Now, how can I add a third column name to that empty df?
>>
>> Normally I would use df$new.col = 1
>>
>> But here I can't use this because it's empty!
>>
>> I tried df$new.col=NULL -- this doesn't give an error but doesn't add the
>> column.
>>
>> Thanks for your help,
>>
>> Emmanuel
>>
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>>
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>
>

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