R help - Dec 2010 - [plyr] Question regarding ddply: use of .(as.name(varname)) and varname in ddply function

Dear R-Helpers:

I am using trying to use *ddply* to extract min and max of a particular
column in a data.frame. I am using two different forms of the function:


## var_name_to_split is a string -- something like "var1" which is the
name
of a column in data.frame

ddply( df, .(as.name(var_name_to_split)), function(x) c(min(x[ , 3] , max(x[
, 3]))) ## fails with an error - case 1
ddply( df, var_name_to_split , function(x) c(min(x[ , 3] , max(x[ , 3])))
               ## works fine - case 2

I can't understand why I get the error in case 1. Can someone help me
please?

Thank you in advance.

S.

----------

Here is the reproducible code:

https://gist.github.com/730069

Here is sample data:

structure(list(g10 = c(1L, 1L, 1L, 10L, 10L, 10L), l1 c(0.410077661080032,
0.607497980054711, 0.640488621149069, -1.47837849145189, -1.48199933642397,
-1.42815840788069), d1 = c(0.917769870675383, 0.959256755797054,
0.772928570498006, 0.473545787883884, 0.590580940273922, 0.0448629265021484
), l13 = c(0.0803696045647364, -0.291741079837731, -0.00191015929550312,
0.295889063381279, 0.615383505686296, 0.71991154637985), d13
c(-1.40821713632015,
-1.27501365601403, -1.41150703235157, 0.708943640186729, 0.276034890463749,
0.663383934998686)), .Names = c("g10", "l1", "d1",
"l13", "d13"
), row.names = c(1L, 2L, 3L, 1758L, 1759L, 1760L), class =
"data.frame")


-----------
If some one doesn't want to open github - here is the code

## Doesn't work

# grp -- name of a column of the the data.frame df
# function call is -- getMinMax1( df1 , grp = "var1")

getMinMax1 <-function(df, grp){
      dfret <- ddply( df , .(as.name(grp)), ## I am using
as.name(grp), source of error
            function(x){
                minmax <- c(mix(x[ , 3]), max(x[ ,3]))
                return(minmax)
            }
            )
      return(dfret)
  }

## Works fine
# grp -- name of a column of the the data.frame df
# function call is -- getMinMax2( df1 , grp = "var1")

getMinMax2 <-function(df, grp){
      dfret <- ddply( df , grp, ## using the quoted variable name
passed to grp when the fun is called
            function(x){
                minmax <- c(min(x[ , 3]), max(x[ ,3]))
                return(minmax)
            }
            )
      return(dfret)
  }

	[[alternative HTML version deleted]]

On 2010-12-06 01:58, Sunny Srivastava wrote:
> Dear R-Helpers:
>
> I am using trying to use *ddply* to extract min and max of a particular
> column in a data.frame. I am using two different forms of the function:
>
>
> ## var_name_to_split is a string -- something like "var1" which
is the name
> of a column in data.frame
>
> ddply( df, .(as.name(var_name_to_split)), function(x) c(min(x[ , 3] ,
max(x[
> , 3]))) ## fails with an error - case 1
> ddply( df, var_name_to_split , function(x) c(min(x[ , 3] , max(x[ , 3])))
>                 ## works fine - case 2
>
Try it without the .(), i.e. ddply(df, as.name(), ....)

Peter Ehlers
> I can't understand why I get the error in case 1. Can someone help me
> please?
>
> Thank you in advance.
>
> S.
>
[ snip ]

Here is another approach to try:
> require(data.table)
> var <- "g10"
> df <- data.table(df)
> str(df)
Classes ?data.table? and 'data.frame':  6 obs. of  5 variables:
 $ g10: int  1 1 1 10 10 10
 $ l1 : num  0.41 0.607 0.64 -1.478 -1.482 ...
 $ d1 : num  0.918 0.959 0.773 0.474 0.591 ...
 $ l13: num  0.08037 -0.29174 -0.00191 0.29589 0.61538 ...
 $ d13: num  -1.408 -1.275 -1.412 0.709 0.276 ...
> df[,list(min=min(d1), max = max(d1)), by = eval(var)]
     g10        min       max
[1,]   1 0.77292857 0.9592568
[2,]  10 0.04486293 0.5905809


On Mon, Dec 6, 2010 at 4:58 AM, Sunny Srivastava
<research.baba at gmail.com> wrote:
> Dear R-Helpers:
>
> I am using trying to use *ddply* to extract min and max of a particular
> column in a data.frame. I am using two different forms of the function:
>
>
> ## var_name_to_split is a string -- something like "var1" which
is the name
> of a column in data.frame
>
> ddply( df, .(as.name(var_name_to_split)), function(x) c(min(x[ , 3] ,
max(x[
> , 3]))) ## fails with an error - case 1
> ddply( df, var_name_to_split , function(x) c(min(x[ , 3] , max(x[ , 3])))
> ? ? ? ? ? ? ? ## works fine - case 2
>
> I can't understand why I get the error in case 1. Can someone help me
> please?
>
> Thank you in advance.
>
> S.
>
> ----------
>
> Here is the reproducible code:
>
> https://gist.github.com/730069
>
> Here is sample data:
>
> structure(list(g10 = c(1L, 1L, 1L, 10L, 10L, 10L), l1 >
c(0.410077661080032,
> 0.607497980054711, 0.640488621149069, -1.47837849145189, -1.48199933642397,
> -1.42815840788069), d1 = c(0.917769870675383, 0.959256755797054,
> 0.772928570498006, 0.473545787883884, 0.590580940273922, 0.0448629265021484
> ), l13 = c(0.0803696045647364, -0.291741079837731, -0.00191015929550312,
> 0.295889063381279, 0.615383505686296, 0.71991154637985), d13 >
c(-1.40821713632015,
> -1.27501365601403, -1.41150703235157, 0.708943640186729, 0.276034890463749,
> 0.663383934998686)), .Names = c("g10", "l1",
"d1", "l13", "d13"
> ), row.names = c(1L, 2L, 3L, 1758L, 1759L, 1760L), class =
"data.frame")
>
>
> -----------
> If some one doesn't want to open github - here is the code
>
> ## Doesn't work
>
> # grp -- name of a column of the the data.frame df
> # function call is -- getMinMax1( df1 , grp = "var1")
>
> getMinMax1 <-function(df, grp){
> ? ? ?dfret <- ddply( df , .(as.name(grp)), ## I am using
> as.name(grp), source of error
> ? ? ? ? ? ?function(x){
> ? ? ? ? ? ? ? ?minmax <- c(mix(x[ , 3]), max(x[ ,3]))
> ? ? ? ? ? ? ? ?return(minmax)
> ? ? ? ? ? ?}
> ? ? ? ? ? ?)
> ? ? ?return(dfret)
> ?}
>
> ## Works fine
> # grp -- name of a column of the the data.frame df
> # function call is -- getMinMax2( df1 , grp = "var1")
>
> getMinMax2 <-function(df, grp){
> ? ? ?dfret <- ddply( df , grp, ## using the quoted variable name
> passed to grp when the fun is called
> ? ? ? ? ? ?function(x){
> ? ? ? ? ? ? ? ?minmax <- c(min(x[ , 3]), max(x[ ,3]))
> ? ? ? ? ? ? ? ?return(minmax)
> ? ? ? ? ? ?}
> ? ? ? ? ? ?)
> ? ? ?return(dfret)
> ?}
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at 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.
>


-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?

On Mon, Dec 6, 2010 at 3:58 AM, Sunny Srivastava
<research.baba at gmail.com> wrote:
> Dear R-Helpers:
>
> I am using trying to use *ddply* to extract min and max of a particular
> column in a data.frame. I am using two different forms of the function:
>
>
> ## var_name_to_split is a string -- something like "var1" which
is the name
> of a column in data.frame
>
> ddply( df, .(as.name(var_name_to_split)), function(x) c(min(x[ , 3] ,
max(x[
> , 3]))) ## fails with an error - case 1
> ddply( df, var_name_to_split , function(x) c(min(x[ , 3] , max(x[ , 3])))
> ? ? ? ? ? ? ? ## works fine - case 2
>
> I can't understand why I get the error in case 1. Can someone help me
> please?
Why do you expect case 1 to work?

Hadley

-- 
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
http://had.co.nz/