R Function to extract columnNames

Hi,
If you are using Rstudio, please check this link (http://support.rstudio.org/help/discussions/problems/850-ddply-misbehaving-in-rstudio-and-only-in-rstudio).
A.K.





----- Original Message -----
From: arun <smartpink111 at yahoo.com>
To: R help <r-help at r-project.org>
Cc: David Winsemius <dwinsemius at comcast.net>
Sent: Wednesday, May 1, 2013 9:49 PM
Subject: Re: R Function to extract columnNames

HI,

I am not sure what is wrong in your side.? I cut and paste the same code and I get this:

library(plyr)
set.seed(25)
?mydf<- data.frame(subid=rep(1:5,each=3),Col=sample(c(0:5,NA),15,replace=TRUE))
?retsample <- function(df, Column,size) {
?set.seed(1234)
?mysel <- ddply(df, .(subid),function(x) summarize(x,missing=sum(is.na(x[[Column]])|x[[Column]]==0)))
?myids<- mysel[mysel$missing==0,1]
?sample_regular<- subset(df,subid%in% sample(myids,size,replace=TRUE))??? 
?return(sample_regular)
?? }
?retsample(mydf,"Col",5) 

?# subid Col
#1????? 1?? 2
#2????? 1?? 4
#3????? 1?? 1
#10???? 4?? 1
#11???? 4?? 2
#12???? 4?? 2


?sessionInfo()
R version 3.0.0 (2013-04-03)
Platform: x86_64-unknown-linux-gnu (64-bit)

locale:
?[1] LC_CTYPE=en_CA.UTF-8?????? LC_NUMERIC=C????????????? 
?[3] LC_TIME=en_CA.UTF-8??????? LC_COLLATE=en_CA.UTF-8??? 
?[5] LC_MONETARY=en_CA.UTF-8??? LC_MESSAGES=en_CA.UTF-8?? 
?[7] LC_PAPER=C???????????????? LC_NAME=C???????????????? 
?[9] LC_ADDRESS=C?????????????? LC_TELEPHONE=C??????????? 
[11] LC_MEASUREMENT=en_CA.UTF-8 LC_IDENTIFICATION=C?????? 

attached base packages:
[1] grid????? stats???? graphics? grDevices utils???? datasets? methods? 
[8] base???? 

other attached packages:
[1] plyr_1.8??????? lattice_0.20-15 chron_2.3-43??? stringr_0.6.2? 
[5] reshape2_1.2.2 


A.K.

David, 
I cut-n-paste and tried to run and I am getting the follwoing error: 
BTW, I really, really appreciate your help. 

library(plyr) 
set.seed(25) 
mydf<- data.frame(subid=rep(1:5,each=3),Col=sample(c(0:5,NA),15,replace=TRUE)) 
retsample <- function(df, Column,size) { 

+ set.seed(1234) 
+ mysel <- ddply(df, .(subid),function(x) summarize(x,missing=sum(is.na(x[[Column]])|x[[Column]]==0))) 
+ myids<- mysel[mysel$missing==0,1] 
+ sample_regular<- subset(df,subid%in% sample(myids,size,replace=TRUE)) ? ? 
+ return(sample_regular) 
+ ? } 

retsample(mydf,"Col",5) 

Error in is.list(by) : 'by' is missing

----- Original Message -----
From: arun <smartpink111 at yahoo.com>
To: R help <r-help at r-project.org>
Cc: David Winsemius <dwinsemius at comcast.net>
Sent: Wednesday, May 1, 2013 4:01 PM
Subject: Re: R Function to extract columnNames

Hi ST,

You could try this:
library(plyr)
set.seed(25)
mydf<- data.frame(subid=rep(1:5,each=3),Col=sample(c(0:5,NA),15,replace=TRUE))
retsample <- function(df, Column,size) {
set.seed(1234)
mysel <- ddply(df, .(subid),function(x) summarize(x,missing=sum(is.na(x[[Column]])|x[[Column]]==0)))
myids<- mysel[mysel$missing==0,1]
sample_regular<- subset(df,subid%in% sample(myids,size,replace=TRUE))??? 
return(sample_regular)
? }
retsample(mydf,"Col",5)
#?? subid Col
#1????? 1?? 2
#2????? 1?? 4
#3????? 1?? 1
#10???? 4?? 1
#11???? 4?? 2
#12???? 4?? 2


A.K.

Thanks David for the tip. I dont think I still have this working for a 

function that i am writing. Say col, subid are column names in my 
dataframe >mydf. My calling function is retsample(mydf,"Col",5)

This below function fails in ddply call. In this call I am counting 

how many nulls or zeros exist for that colum that I am passing. I get 
"Error in >eval(expr, envir, enclos) : object 'myCol' not found"

#Get appropriate random sample to print for variable col from dataframe df, that has 0 missing values 
retsample <- function(df,x,size ) { 

?> ? ? set.seed(1234) 
? >? ? myCol <- df[[x]] 
? >? ? mysel <- ddply(df,c("subid"),summarise,missing=sum(is.na(myCol)| myCol==0)) 
? >? ? #select subjects with no missing values 
? >? ? myids <- mysel[mysel$missing==0,1] 
? >? ? sample_regular <- subset(df,subid %in% sample(myids, size=size)) 
? >? ? return(sample_regular)

} 

Thank You for your assistance. 
-ST 

----- Original Message -----
From: arun <smartpink111 at yahoo.com>
To: R help <r-help at r-project.org>
Cc: 
Sent: Tuesday, April 30, 2013 9:00 AM
Subject: Re: R Function to extract columnNames

Hi,
May be this helps:
funcName<- function(df1, x){
?whatCol=df1[[x]]
?print("Got it")
?print(whatCol)
?}
?
funcName(df,"ColA")
#[1] "Got it"
#[1] 1 2 3 4 5
? funcName(df,"ColB")
#[1] "Got it"
#[1] A B C D E
#Levels: A B C D E


A.K.

I am trying to extract the 2nd column from a dataframe using a function 

called funcName. Note this is an example that I need cos I am using it 
to >read the values I pass into a function call - these passed values 
represent dataframe column names. I am trying to use this concept for a 
vary large >dataframe with 100+ columns.

ColA <- c(1,2,3,4,5) 
ColB <- c("A","B","C","D","E") 
df <- data.frame(ColA,ColB) 

funcName <- function(x) { 
whatCol = paste("df",x,sep="$") 

?>print("Got it",whatCol)

} 

funcName("ColA") 

Please advise, since this code is not working. Thanks in advance. 

-ST