R help - Oct 2012 - Excluding all teh columns from a data frame if the standard deviation of that column is zero(0).

Hi All,

  I have a data frame where nearly 10K columns of data, where most of them
have standard deviation( of all rows) as zero.
I want to exclude all the columns from the data frame and proceed to further
processing.

I tried like blow.  
*data <- read.csv("data.CSV", header=T)

for(i in 2:ncol(data))
 if(sd(data[,i])==0){
 df[,i] <-NULL
}
*
where I have the data columns from 2:ncol, but getting the error "Error in
df[, i] <- NULL : object of type 'closure' is not subsettable"

Can any one suggest the right method to accomplish this.






-----
Sidda
Business Analyst Lead
Applied Materials Inc.

--
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On Tue, Oct 16, 2012 at 9:08 AM, siddu479 <onlyfordigitalstuff at
gmail.com> wrote:
> Hi All,
>
>   I have a data frame where nearly 10K columns of data, where most of them
> have standard deviation( of all rows) as zero.
> I want to exclude all the columns from the data frame and proceed to
further
> processing.
>
> I tried like blow.
> *data <- read.csv("data.CSV", header=T)
>
> for(i in 2:ncol(data))
>  if(sd(data[,i])==0){
>  df[,i] <-NULL
> }
> *
> where I have the data columns from 2:ncol, but getting the error
"Error in
> df[, i] <- NULL : object of type 'closure' is not
subsettable"
>
> Can any one suggest the right method to accomplish this.
>
A perfect example of why "df" is a bad function name. Here you are
getting the function ( = closure, more or less) df, density function
of the F distribution, instead of the uninitialized variable "df".
Since the function can't be subsetted, you get the error.

In fact, I think you really just want this one liner:

!(apply(data, 2, sd) == 0)

which can be used to subset.

In the same vein as the df problem, data is also a bad function name
(it's also a pre-defined function used for loading, surprise
surprise!, data) but R is smart enough to keep them straight in this
simple example. In your real script, however, I'd strongly suggest you
change it.

Cheers,
Michael

Hello,

You're calling your dataset 'data' and 'df' in the same
instruction,
hence the error. (Even if you were to call it different names in 
different instructions...)

Also, both 'data' and 'df' are really bad names for objects,
they're
already are R functions. Name your dataset something else. And be 
consistent in the use of that name.

Hope this helps,

Rui Barradas
Em 16-10-2012 09:08, siddu479 escreveu:
> Hi All,
>
>    I have a data frame where nearly 10K columns of data, where most of them
> have standard deviation( of all rows) as zero.
> I want to exclude all the columns from the data frame and proceed to
further
> processing.
>
> I tried like blow.
> *data <- read.csv("data.CSV", header=T)
>
> for(i in 2:ncol(data))
>   if(sd(data[,i])==0){
>   df[,i] <-NULL
> }
> *
> where I have the data columns from 2:ncol, but getting the error
"Error in
> df[, i] <- NULL : object of type 'closure' is not
subsettable"
>
> Can any one suggest the right method to accomplish this.
>
>
>
>
>
>
> -----
> Sidda
> Business Analyst Lead
> Applied Materials Inc.
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/Excluding-all-teh-columns-from-a-data-frame-if-the-standard-deviation-of-that-column-is-zero-0-tp4646310.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> 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.

HI,
May be this helps. 

set.seed(1)
?dat1<-data.frame(col1=rep(5,10),col2=rnorm(10,15),col3=rep(25,10),col4=rnorm(10,25))
?dat1[sapply(dat1,function(x) sd(x)!=0)]
#?????? col2???? col4
#1? 14.37355 26.51178
#2? 15.18364 25.38984
#3? 14.16437 24.37876
#4? 16.59528 22.78530
#5? 15.32951 26.12493
#6? 14.17953 24.95507
#7? 15.48743 24.98381
#8? 15.73832 25.94384
#9? 15.57578 25.82122
#10 14.69461 25.59390
A.K.




----- Original Message -----
From: siddu479 <onlyfordigitalstuff at gmail.com>
To: r-help at r-project.org
Cc: 
Sent: Tuesday, October 16, 2012 4:08 AM
Subject: [R] Excluding all teh columns from a data frame if the standard
deviation of that column is zero(0).

Hi All,

? I have a data frame where nearly 10K columns of data, where most of them
have standard deviation( of all rows) as zero.
I want to exclude all the columns from the data frame and proceed to further
processing.

I tried like blow.? 
*data <- read.csv("data.CSV", header=T)

for(i in 2:ncol(data))
if(sd(data[,i])==0){
df[,i] <-NULL
}
*
where I have the data columns from 2:ncol, but getting the error "Error in
df[, i] <- NULL : object of type 'closure' is not subsettable"

Can any one suggest the right method to accomplish this.






-----
Sidda
Business Analyst Lead
Applied Materials Inc.

--
View this message in context:
http://r.789695.n4.nabble.com/Excluding-all-teh-columns-from-a-data-frame-if-the-standard-deviation-of-that-column-is-zero-0-tp4646310.html
Sent from the R help mailing list archive at Nabble.com.

______________________________________________
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.