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extracting the last row of each group in a data frame

9 messages · Hao Cen, Baptiste Auguie, Jorge Ivan Velez +5 more

Hao Cen
# 
Hi,

I would like to extract the last row of each group in a data frame.

The data frame is as follows

Name Value
A 1
A 2
A 3
B 4
B 8
C 2
D 3

I would like to get a data frame as
Name Value
A 3
B 8
C 2
D 3

Thank you for your suggestions in advance

Jeff
Baptiste Auguie
# 
Hi,

You could try plyr,

library(plyr)

ddply(d,.(Name), tail,1)

  Name Value
1    A     3
2    B     8
3    C     2
4    D     3

HTH,

baptiste

2009/11/16 Hao Cen <hcen at andrew.cmu.edu>:
David Winsemius
#
On Nov 16, 2009, at 2:42 PM, Hao Cen wrote:

            

      
      
      
    

        
by(dfname$Value, dfname$Name, tail, 1) #which gets you a list

Or:

aggregate(dfname$Value, list(dfname$Name), tail, 1)  #which returns a  
data.frame
   Group.1 x
1       A 3
2       B 8
3       C 2
4       D 3

            

      
      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Charlie Sharpsteen
    

    

      
      #
    

  


  

      
jeffc wrote:

            

      
      
      
    

        
Try using the base function by() or ddply() from Hadley Wickham's plyr
package:

  require( plyr )

  tstData <- structure(list(Name = structure(c(1L, 1L, 1L, 2L, 2L, 3L, 4L),
.Label = c("A", 
"B", "C", "D"), class = "factor"), Value = c(1L, 2L, 3L, 4L, 
8L, 2L, 3L)), .Names = c("Name", "Value"), class = "data.frame", row.names =
c(NA, 
-7L))

  lastRows <- ddply( tstData, 'Name', function( group ){

    return(
      data.frame( Value = tail( group[['Value']], n = 1 ) )
    )

  })

  lastRows
    Name Value
  1    A     3
  2    B     8
  3    C     2
  4    D     3


Hope this helps!


-Charlie


-----
Charlie Sharpsteen
Undergraduate
Environmental Resources Engineering
Humboldt State University

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Peter Ehlers
    

    

      
      #
    

  


  

      
I would use pkg:plyr, but just to show how
versatile R is:

ind <- cumsum(rle(as.numeric(dat$Name))$lengths)
dat[ind, ]

where I'm assuming that your data frame is
called 'dat'.

  -Peter Ehlers

        
Hao Cen wrote:

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Gabor Grothendieck
    

    

      
      #
    

  


  

      
Try this:

            

      
      
      
    

        
Name Value
1    A     3
2    B     8
3    C     2
4    D     3

        
On Mon, Nov 16, 2009 at 2:42 PM, Hao Cen <hcen at andrew.cmu.edu> wrote:

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Hao Cen
    

    

      
      #
    

  


  

      
Thanks to all who helped. These are all great suggestions. 

Jeff

-----Original Message-----
From: Gabor Grothendieck [mailto:ggrothendieck at gmail.com] 
Sent: Monday, November 16, 2009 6:27 PM
To: Hao Cen
Cc: r-help at r-project.org
Subject: Re: [R] extracting the last row of each group in a data frame

Try this:

            

      
      
      
    

        
Name Value
1    A     3
2    B     8
3    C     2
4    D     3

        
On Mon, Nov 16, 2009 at 2:42 PM, Hao Cen <hcen at andrew.cmu.edu> wrote:

            

      
      
      
    

        

      
      
    

        
http://www.R-project.org/posting-guide.html

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Nutter, Benjamin
    

    

      
      #
    

  


  

      
I usually use the following function:

last.record <- function(data, id, ..., na.last=TRUE, decreasing=FALSE){

  #*** Make vector of variables to sort by
  v <- c(id, unlist(list(...)))

  #*** Sort Data Frame
  data <- data[do.call(order,
            c(data[,v, drop=FALSE], na.last=na.last,
decreasing=decreasing)),]

  #*** Extract last record for each id
  data[!duplicated(data[,id], fromLast=TRUE),]
}


Data        Data Frame from which the record is to be extracted
Id          ID variable from which the record is to be extracted.  The
data frame is automatically
	      sorted by this variable.  May be either a character string
or an integer.
...         Names of variables (or indices) in additon to id by which
data should be sorted.
na.last     Argument passed to order().  Determines if missing values
are placed at the end
	      of the sorting.
Decreasing  Argument passed to order().  Determines if data frame is
sorted in descending
	      order.



So, in your example

            

      
      
      
    

        
Value = c(1, 2, 3, 4, 8, 2, 3))

            

      
      
      
    

        
-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Hao Cen
Sent: Monday, November 16, 2009 2:43 PM
To: r-help at r-project.org
Subject: [R] extracting the last row of each group in a data frame

Hi,

I would like to extract the last row of each group in a data frame.

The data frame is as follows

Name Value
A 1
A 2
A 3
B 4
B 8
C 2
D 3

I would like to get a data frame as
Name Value
A 3
B 8
C 2
D 3

Thank you for your suggestions in advance

Jeff

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http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.


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