Re: [R] data frame manipulation with zero rows

Peter Ehlers Tue, 01 Jun 2010 03:09:02 -0700

On 2010-06-01 1:53, arnaud Gaboury wrote:

Brian,


If I do understand correctly, I must use in my function something else than
ddply() if I want to avoid any error each time my df has zero rows?
Am I correct?


You could define a function to handle the zero-rows case:

f <- function(x){
 if(nrow(x) < 1) out <- x[, c(1,3,2)]  # or whatever
 else
   out <- ddply(x, c("DESCRIPTION","SETTLEMENT"), summarise,
                    POSITION=sum(QUANTITY))[,c(1,3,2)]
 out
}
f(futures)

 -Peter Ehlers

-----Original Message-----
From: Prof Brian Ripley [mailto:rip...@stats.ox.ac.uk]
Sent: Tuesday, June 01, 2010 9:47 AM
To: arnaud Gaboury
Subject: Re: [R] data frame manipulation with zero rows

On Tue, 1 Jun 2010, arnaud Gaboury wrote:

Dear group,

Here is the kind of data.frame I obtain every day with my function :

futures<-
structure(list(DESCRIPTION = c("CORN Jul/10", "CORN Jul/10",
"CORN Jul/10", "CORN Jul/10", "CORN Jul/10", "LIVE CATTLE Aug/10",
"LIVE CATTLE Aug/10", "SUGAR NO.11 Jul/10", "SUGAR NO.11 Jul/10",
"SUGAR NO.11 Jul/10", "SUGAR NO.11 Jul/10", "SUGAR NO.11 Jul/10"
), CREATED.DATE = structure(c(18403, 18406, 18406, 18406, 18406,
18407, 18408, 18406, 18407, 18407, 18407, 18407), class = "Date"),
    QUANTITY = c(1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1), SETTLEMENT =
c("373.2500",
    "373.2500", "373.2500", "373.2500", "373.2500", "90.7750",
    "90.7750", "14.9200", "14.9200", "14.9200", "14.9200", "14.9200"
    )), .Names = c("DESCRIPTION", "CREATED.DATE", "QUANTITY",
"SETTLEMENT"), row.names = c(NA, 12L), class = "data.frame")

I need then to apply to the df this following code line :

PosFut=ddply(futures, c("DESCRIPTION","SETTLEMENT"), summarise,

POSITION=

sum(QUANTITY))[,c(1,3,2)]

It works perfectly in most of case, BUT I have a new problem: it can
sometime occurs that my df "futures" is empty, with zero rows.


futures<-
structure(list(DESCRIPTION = character(0), CREATED.DATE =
structure(numeric(0), class = "Date"),
    QUANTITY = numeric(0), SETTLEMENT = character(0)), .Names =
c("DESCRIPTION",
"CREATED.DATE", "QUANTITY", "SETTLEMENT"), row.names = integer(0),

class =

"data.frame")

It is not the usual case, but it can happen. With this df, when I

pass the

above mentione line, I get an error :

PosFut=ddply(futures, c("DESCRIPTION","SETTLEMENT"), summarise,

POSITION=

sum(QUANTITY))[,c(1,3,2)]
Error in tapply(1:nrow(data), splitv, list) :
  arguments must have same length


How can I avoid this when my df is empty?


Ask the author of the (missing) function ddply() to correct the error
of using 1:nrow(data) by replacing it by seq_len(nrow(data)).

It's helpful to give example code, but much more helpful if you test
it: yours cannot work without the function ddply() -- this is what
'self-contained' means in the footer here.


Any help is appreciated

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--
Brian D. Ripley,                  rip...@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595


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

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