R help - Jul 2006 - 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.

thanks in advance,
Daryl.

On Sun, 9 Jul 2006, Daryl Manning wrote:
> 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.
Did you use numeric NA?  That is the way to so this, so you will need to 
give a reproducible example (as the posting guide asks).

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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