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