[R] How to get R to ignore certain values when analyzing a column in a data table ?

[Petr Pikal]

Hi

On 9 Jul 2006 at 20:01, Daryl Manning wrote:

To:             	r-help at stat.math.ethz.ch
From:           	Daryl Manning <dwm at wakatara.com>
Date sent:      	Sun, 9 Jul 2006 20:01:10 -0700
Subject:        	[R] How to get R to ignore certain values when analyzing a column
	in a data table ?

> Apologies if this is in (one of the many) manuals somewhere... Trying 
> to switch to R from other stats programs.
> 
> Basically, I have a large data table I've dumped from a DB, some of 
> the values which are nulls '-' which I've converted to zeros. I've 
> read it in using read.table fine.
> 
> I want R to ignore the zero values when graphing or doing various 
> other calculations.
> 
> Is there a way to do this ?
> 
> I did try to use NA but kept getting errors that x must be numeric.

What does str(your.data) says about your data? I presume it is 
factor.

datafr <- data.frame(a=rnorm(10), b=rnorm(10))
datafr[3,1]<-0

> datafr$a
 [1] -0.1645236 -0.2533617  0.0000000  0.5566632 -0.6887557 -
0.7074952  0.3645820  0.7685329 -0.1123462  0.8811077

> mean(datafr$a)
[1] 0.06444035

> datafr$a==0
 [1] FALSE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE

> datafr$a[datafr$a==0]
[1] 0

> datafr$a[datafr$a==0]<-NA

> mean(datafr$a)
[1] NA

> mean(datafr$a, na.rm=T)
[1] 0.07160039
>

works OK.

HTH
Petr


> 
> thanks in advance,
> Daryl.
> 
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Petr Pikal
petr.pikal at precheza.cz