[R] Remove columns from dataframe based on their statistics

[arun]

HI,

I tweaked the code of James a little bit to produce the same result.
> for(i in seq(ncol(df),1))
 if(sd(df[,i])==0){
 df[,i] <-NULL
 }





----- Original Message -----
From: J Toll <jctoll at gmail.com>
To: Johannes Radinger <JRadinger at gmx.at>
Cc: R-help at r-project.org
Sent: Thursday, May 31, 2012 9:52 AM
Subject: Re: [R] Remove columns from dataframe based on their statistics
On Thu, May 31, 2012 at 8:27 AM, Johannes Radinger <JRadinger at gmx.at> wrote:
> Hi,
>
> I have a dataframe and want to remove columns from it
> that are populated with a similar value (for the total
> column) (the variation of that column is 0). Is there an
> easier way than to calculate the statistics and then
> remove them by hand?
>
> A <- runif(100)
> B <- rep(1,100)
> C <- rep(2.42,100)
> D <- runif(100)
> df <- data.frame(A,B,C,D) # if want to conditionally remove column B and C as they show no variations


You could try something like:

for (i in seq(ncol(df), 1))
  if (length(unique(df[, i])) == 1) {
  df[, i] <- NULL
}

or for just numeric values:

for (i in seq(ncol(df), 1))
  if (all(mean(df[, i]) == df[, i])) {
  df[, i] <- NULL
}

HTH,

James

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