R help - Jun 2004 - The "median" function in R does not work properly.

Hi, 

 

1.) The "median" function does not work well.  Please refer to the
data
below (same data is attached as txt-delimited).  This is what I try to
do in R:

 

median ( dataf [2:9] )  

 

I get warning:  "needs numeric data"

 

2.) BUT if apply the median to a single vector: 

 

median ( dataf [,2]] )

 

then it works:

 

 

3.) How come the "median" function does not let me take the median of
all 8 vectors at once?  Obviously, if I can perform the test on a single
array, then it means I have numeric data because I do not get warning.
Also, if I look at the "mode" for each array I get
"numeric".

 

 

Probe 1

256

589

308

698

745

850

750

1200

Probe 2

225

422

350

625

400

650

852

1400

Probe 3

295

530

325

585

350

700

752

1100

Probe 4

300

450

425

430

700

645

735

1250

 

 

Thanks in advance,

 

 

Alexi Zubiria

Technical Support Specialist

Silicon Genetics

2601 Spring Street

Redwood City CA, 94063

Main: 650-367-9600

Support: 866-744-7638

alexi@silicongenetics.com

 


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On Thu, 24 Jun 2004 13:23:22 -0700, "Alexi Zubiria"
<alexi at silicongenetics.com> wrote :
>Hi, 
>
> 
>
>1.) The "median" function does not work well.  
It works fine for me.  You were trying to take the median of a list.
It only knows how to take the median of a vector.

Use dataf [,2:9] not dataf [2:9] to get a vector.

Duncan Murdoch

Oops, missed something below:

On Thu, 24 Jun 2004 13:23:22 -0700, "Alexi Zubiria"
<alexi at silicongenetics.com> wrote :
>Hi, 
>
> 
>
>1.) The "median" function does not work well.  
It works fine for me.  You were trying to take the median of a list.
It only knows how to take the median of a vector of numbers.

Use as.matrix(dataf [,2:9]) not dataf [2:9] to get a numeric matrix
(which is a vector of numbers).

Duncan Murdoch

Alexi Zubiria wrote:
> Hi, 
> 
>  
> 
> 1.) The "median" function does not work well.  Please refer to
the data
> below (same data is attached as txt-delimited).  This is what I try to
> do in R:
> 
>  
> 
> median ( dataf [2:9] )  
> 
>  
> 
> I get warning:  "needs numeric data"
> 
>  
> 
> 2.) BUT if apply the median to a single vector: 
> 
>  
> 
> median ( dataf [,2]] )
> 
>  
> 
> then it works:
> 
>  
> 
>  
> 
> 3.) How come the "median" function does not let me take the
median of
> all 8 vectors at once?  Obviously, if I can perform the test on a single
> array, then it means I have numeric data because I do not get warning.
> Also, if I look at the "mode" for each array I get
"numeric".
> 
>  
> 
> 
median *does* work properly and as documented:

Arguments:

        x: a numeric vector containing the values whose median is to be
           computed.

so you supplied a `list' or `data.frame' not a vector. I'm not sure
what
you expected, but if you want to obtain the median of each column in 
your matrix, then use ?apply:

apply(as.matrix(dataf), 2, median)

Or if you want to get the median of all vectors (a single number) then use

median(as.matrix(dataf))

I assume from your post you supplied a data.frame, however if dataf 
really is a matrix (try data.class(dataf)) then median(dataf) will 
accomplish the last line (at least on R-1.9.1 for win2000).

--sundar