Re: [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  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 
> 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
>>
>> [[alternative HTML version deleted]]
>>
>> __
>> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posti
>> ng-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>

[[alternative HTML version deleted]]

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

[S Ellison]

> Now, how can I add a third column name to that empty df?
You could use functions that generate zero-length objects. Examples:


df$newv <- vector(mode="numeric") #logical by default, so <-vector() would give 
you a zero-length logical

df$newi <- integer()

df$newf <- factor()


S Ellison



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

[PIKAL Petr]

Hi

data frames are structures which need to have the same length of all variables. 
So if you have 0 length variables you need to add also 0 length vectors

> df$aa<-numeric(length=0)
> df
[1] id   data aa
<0 rows> (or 0-length row.names)
> df$bb<-character(length=0)
> df
[1] id   data aa   bb
<0 rows> (or 0-length row.names)

However it seems to me that you are asking for trouble. Incremental increase 
size of data frame is rarely needed and probably result of bad programming 
practice.

Cheers
Petr

> -Original Message-
> From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Emmanuel
> Levy
> Sent: Wednesday, November 2, 2016 2:48 PM
> To: r-h...@stat.math.ethz.ch
> Subject: [R] Adding a column to an **empty** data.frame
>
> 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
>
>   [[alternative HTML version deleted]]
>
> __
> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.


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

[Emmanuel Levy]

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

[[alternative HTML version deleted]]

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

[William Dunlap via R-help]

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 
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
>
> [[alternative HTML version deleted]]
>
> __
> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
>

[[alternative HTML version deleted]]

__
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.