R help - Nov 2016 - 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]]

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
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at 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]]

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
>>
>>         [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help at 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]]

> 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



*******************************************************************
This email and any attachments are confidential. Any use...{{dropped:8}}

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-bounces at r-project.org] On Behalf Of Emmanuel
> Levy
> Sent: Wednesday, November 2, 2016 2:48 PM
> To: r-help at 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 at 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.
________________________________
Tento e-mail a jak?koliv k n?mu p?ipojen? dokumenty jsou d?v?rn? a jsou ur?eny
pouze jeho adres?t?m.
Jestli?e jste obdr?el(a) tento e-mail omylem, informujte laskav? neprodlen? jeho
odes?latele. Obsah tohoto emailu i s p??lohami a jeho kopie vyma?te ze sv?ho
syst?mu.
Nejste-li zam??len?m adres?tem tohoto emailu, nejste opr?vn?ni tento email
jakkoliv u??vat, roz?i?ovat, kop?rovat ?i zve?ej?ovat.
Odes?latel e-mailu neodpov?d? za eventu?ln? ?kodu zp?sobenou modifikacemi ?i
zpo?d?n?m p?enosu e-mailu.

V p??pad?, ?e je tento e-mail sou??st? obchodn?ho jedn?n?:
- vyhrazuje si odes?latel pr?vo ukon?it kdykoliv jedn?n? o uzav?en? smlouvy, a
to z jak?hokoliv d?vodu i bez uveden? d?vodu.
- a obsahuje-li nab?dku, je adres?t opr?vn?n nab?dku bezodkladn? p?ijmout;
Odes?latel tohoto e-mailu (nab?dky) vylu?uje p?ijet? nab?dky ze strany p??jemce
s dodatkem ?i odchylkou.
- trv? odes?latel na tom, ?e p??slu?n? smlouva je uzav?ena teprve v?slovn?m
dosa?en?m shody na v?ech jej?ch n?le?itostech.
- odes?latel tohoto emailu informuje, ?e nen? opr?vn?n uzav?rat za spole?nost
??dn? smlouvy s v?jimkou p??pad?, kdy k tomu byl p?semn? zmocn?n nebo p?semn?
pov??en a takov? pov??en? nebo pln? moc byly adres?tovi tohoto emailu p??padn?
osob?, kterou adres?t zastupuje, p?edlo?eny nebo jejich existence je adres?tovi
?i osob? j?m zastoupen? zn?m?.

This e-mail and any documents attached to it may be confidential and are
intended only for its intended recipients.
If you received this e-mail by mistake, please immediately inform its sender.
Delete the contents of this e-mail with all attachments and its copies from your
system.
If you are not the intended recipient of this e-mail, you are not authorized to
use, disseminate, copy or disclose this e-mail in any manner.
The sender of this e-mail shall not be liable for any possible damage caused by
modifications of the e-mail or by delay with transfer of the email.

In case that this e-mail forms part of business dealings:
- the sender reserves the right to end negotiations about entering into a
contract in any time, for any reason, and without stating any reasoning.
- if the e-mail contains an offer, the recipient is entitled to immediately
accept such offer; The sender of this e-mail (offer) excludes any acceptance of
the offer on the part of the recipient containing any amendment or variation.
- the sender insists on that the respective contract is concluded only upon an
express mutual agreement on all its aspects.
- the sender of this e-mail informs that he/she is not authorized to enter into
any contracts on behalf of the company except for cases in which he/she is
expressly authorized to do so in writing, and such authorization or power of
attorney is submitted to the recipient or the person represented by the
recipient, or the existence of such authorization is known to the recipient of
the person represented by the recipient.