[R] ddply - how to transform df column in place

2011-08-23 Thread jjap 
Dear R-users,

I am trying to get the plyr syntax right, without much success.

Given:
d- data.frame(cbind(x=1,y=seq(20100801,20100830,1)))
names(d)-c(first, daterep)
d2-d

# I can convert the daterep column in place the classic way:
d$daterep-as.Date(strptime(d$daterep, format=%Y%m%d))

# How to do it the plyr way?
ddply(d2, c(daterep), function(df){as.Date(df, format=%Y%m%d)})
# returns: Error in as.Date.default(df, format = %Y%m%d) : 
#   do not know how to convert 'df' to class Date

Thanks for any hints,

---jean

--
View this message in context: 
http://r.789695.n4.nabble.com/ddply-how-to-transform-df-column-in-place-tp3764037p3764037.html
Sent from the R help mailing list archive at Nabble.com.

__
R-help@r-project.org mailing list
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.

Re: [R] ddply - how to transform df column in place

2011-08-23 Thread Ista Zahn 
Hi Jean,

On Tue, Aug 23, 2011 at 6:16 PM, jjap jean.plamon...@fpinnovations.ca wrote:
 Dear R-users,

 I am trying to get the plyr syntax right, without much success.

 Given:
 d- data.frame(cbind(x=1,y=seq(20100801,20100830,1)))
 names(d)-c(first, daterep)
 d2-d

 # I can convert the daterep column in place the classic way:
 d$daterep-as.Date(strptime(d$daterep, format=%Y%m%d))

 # How to do it the plyr way?
 ddply(d2, c(daterep), function(df){as.Date(df, format=%Y%m%d)})
 # returns: Error in as.Date.default(df, format = %Y%m%d) :
 #   do not know how to convert 'df' to class Date

There is no plyr way to do this, as this is not the kind of
operation plyr is designed to carry out. plyr is designed to simplify
the process of 1) splitting the data into groups, 2) operating on each
group, and 3) putting the results back together. Since your example
does not involve this kind of split-apply-combine approach plyr will
not help you.

HTH,
Ista


 Thanks for any hints,

 ---jean

 --
 View this message in context: 
 http://r.789695.n4.nabble.com/ddply-how-to-transform-df-column-in-place-tp3764037p3764037.html
 Sent from the R help mailing list archive at Nabble.com.

 __
 R-help@r-project.org mailing list
 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.




-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org

__
R-help@r-project.org mailing list
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.

Re: [R] ddply - how to transform df column in place

2011-08-23 Thread Justin Haynes 
Jean,

Ista is right, but:

In your function you are asking as.Date to convert the whole data.frame df
rather than just your daterep column.

out-ddply(d2, .(daterep), function(df)
as.Date(strptime(df$daterep,format='%Y%m%d')))
str(out)
'data.frame':30 obs. of  2 variables:
 $ daterep: num  20100801 20100802 20100803 20100804 20100805 ...
 $ V1 : Date, format: 2010-08-01 2010-08-02 2010-08-03
2010-08-04 ...


On Tue, Aug 23, 2011 at 3:16 PM, jjap jean.plamon...@fpinnovations.cawrote:

 Dear R-users,

 I am trying to get the plyr syntax right, without much success.

 Given:
 d- data.frame(cbind(x=1,y=seq(20100801,20100830,1)))
 names(d)-c(first, daterep)
 d2-d

 # I can convert the daterep column in place the classic way:
 d$daterep-as.Date(strptime(d$daterep, format=%Y%m%d))

 # How to do it the plyr way?
 ddply(d2, c(daterep), function(df){as.Date(df, format=%Y%m%d)})
 # returns: Error in as.Date.default(df, format = %Y%m%d) :
 #   do not know how to convert 'df' to class Date

 Thanks for any hints,

 ---jean

 --
 View this message in context:
 http://r.789695.n4.nabble.com/ddply-how-to-transform-df-column-in-place-tp3764037p3764037.html
 Sent from the R help mailing list archive at Nabble.com.

 __
 R-help@r-project.org mailing list
 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
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.

Re: [R] ddply - how to transform df column in place

2011-08-23 Thread David Winsemius 


On Aug 23, 2011, at 6:16 PM, jjap wrote:


Dear R-users,

I am trying to get the plyr syntax right, without much success.

Given:
d- data.frame(cbind(x=1,y=seq(20100801,20100830,1)))
names(d)-c(first, daterep)
d2-d

# I can convert the daterep column in place the classic way:
d$daterep-as.Date(strptime(d$daterep, format=%Y%m%d))

# How to do it the plyr way?
ddply(d2, c(daterep), function(df){as.Date(df, format=%Y%m%d)})
# returns: Error in as.Date.default(df, format = %Y%m%d) :
#   do not know how to convert 'df' to class Date


I'm pretty sure that when you do that you are sending dataframes to  
'x' that have been split apart on the basis of their daterep values.  
Why should there be a plyr way of converting types when there is no  
splitting of dataframes needed?


If you wanted nevertheless to do it the plyr way:

d2 - ddply(d, NULL , transform,
daterep =  as.Date(strptime(d$daterep, format=%Y%m%d))

--

David Winsemius, MD
West Hartford, CT

__
R-help@r-project.org mailing list
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.

Re: [R] ddply - how to transform df column in place

2011-08-23 Thread David Winsemius 


On Aug 23, 2011, at 6:38 PM, David Winsemius wrote:



On Aug 23, 2011, at 6:16 PM, jjap wrote:


Dear R-users,

I am trying to get the plyr syntax right, without much success.

Given:
d- data.frame(cbind(x=1,y=seq(20100801,20100830,1)))
names(d)-c(first, daterep)
d2-d

# I can convert the daterep column in place the classic way:
d$daterep-as.Date(strptime(d$daterep, format=%Y%m%d))

# How to do it the plyr way?
ddply(d2, c(daterep), function(df){as.Date(df, format=%Y%m%d)})
# returns: Error in as.Date.default(df, format = %Y%m%d) :
#   do not know how to convert 'df' to class Date


I'm pretty sure that when you do that you are sending dataframes to  
'x' that have been split apart on the basis of their daterep values.  
Why should there be a plyr way of converting types when there is  
no splitting of dataframes needed?


If you wanted nevertheless to do it the plyr way:

d2 - ddply(d, NULL , transform,
   daterep =  as.Date(strptime(d$daterep, format=%Y%m%d))


Make that:
d2 - ddply(d, NULL , transform,
   daterep =  as.Date(strptime(daterep, format=%Y%m%d)) )
d2# you do get an unnecessary column




--

David Winsemius, MD
West Hartford, CT

__
R-help@r-project.org mailing list
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.


David Winsemius, MD
West Hartford, CT

__
R-help@r-project.org mailing list
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.