R help - May 2007 - more woes trying to convert a data.frame to a numerical matrix

I have the following csv file:

name,x,y,z
category,delta,gamma,epsilon
a,1,2,3
b,4,5,6
c,7,8,9

I'd like to create a numeric matrix of just the numbers in this csv dataset.

I've tried the following program:

sample.data <- read.csv("sample.csv")
numerical.data <- as.matrix(sample.data[-1,-1])

However, print(numerical.data) returns what appears to be a matrix of
characters:

  x   y   z
2 "1" "2" "3"
3 "4" "5" "6"
4 "7" "8" "9"

How do I force it to be numbers rather than characters?

Thanks,
Andrew

	[[alternative HTML version deleted]]

?as.numeric

------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Reseach Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
Thierry.Onkelinx op inbo.be
www.inbo.be 

Do not put your faith in what statistics say until you have carefully
considered what they do not say.  ~William W. Watt
A statistical analysis, properly conducted, is a delicate dissection of
uncertainties, a surgery of suppositions. ~M.J.Moroney

 
> -----Oorspronkelijk bericht-----
> Van: r-help-bounces op stat.math.ethz.ch 
> [mailto:r-help-bounces op stat.math.ethz.ch] Namens Andrew Yee
> Verzonden: woensdag 16 mei 2007 14:11
> Aan: r-help op stat.math.ethz.ch
> Onderwerp: [R] more woes trying to convert a data.frame to a 
> numerical matrix
> 
> I have the following csv file:
> 
> name,x,y,z
> category,delta,gamma,epsilon
> a,1,2,3
> b,4,5,6
> c,7,8,9
> 
> I'd like to create a numeric matrix of just the numbers in 
> this csv dataset.
> 
> I've tried the following program:
> 
> sample.data <- read.csv("sample.csv")
> numerical.data <- as.matrix(sample.data[-1,-1])
> 
> However, print(numerical.data) returns what appears to be a matrix of
> characters:
> 
>   x   y   z
> 2 "1" "2" "3"
> 3 "4" "5" "6"
> 4 "7" "8" "9"
> 
> How do I force it to be numbers rather than characters?
> 
> Thanks,
> Andrew
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help op stat.math.ethz.ch 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.
>

On Wed, 2007-05-16 at 08:10 -0400, Andrew Yee wrote:
> I have the following csv file:
> 
> name,x,y,z
> category,delta,gamma,epsilon
> a,1,2,3
> b,4,5,6
> c,7,8,9
> 
> I'd like to create a numeric matrix of just the numbers in this csv
dataset.
> 
> I've tried the following program:
> 
> sample.data <- read.csv("sample.csv")
> numerical.data <- as.matrix(sample.data[-1,-1])
> 
> However, print(numerical.data) returns what appears to be a matrix of
> characters:
> 
>   x   y   z
> 2 "1" "2" "3"
> 3 "4" "5" "6"
> 4 "7" "8" "9"
> 
> How do I force it to be numbers rather than characters?
> 
> Thanks,
> Andrew
The problem is that you have two rows which contain alpha entries. 

The first row is treated as the header, but the second row is treated as
actual data, thus overriding the numeric values in the subsequent rows.

You could use:

  as.numeric(as.matrix(sample.data[-1, -1]))

to coerce the matrix to numeric, or if you don't need the alpha entries,
you could modify the read.csv() call to something like:

  read.csv("sample.csv", header = FALSE, skip = 2, row.names = 1, 
           col.names = c("name", "x", "y",
"z")

This will skip the first two rows, set the first column to the row names
and give you a data frame with numeric columns, which in most cases can
be treated as a numeric matrix and/or you could explicitly coerce it to
one.

HTH,

Marc Schwartz

have a look at: ?as.numeric() and ?data.matrix().


I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://med.kuleuven.be/biostat/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Andrew Yee" <andrewjyee at gmail.com>
To: <r-help at stat.math.ethz.ch>
Sent: Wednesday, May 16, 2007 2:10 PM
Subject: [R] more woes trying to convert a data.frame to a numerical 
matrix

>I have the following csv file:
>
> name,x,y,z
> category,delta,gamma,epsilon
> a,1,2,3
> b,4,5,6
> c,7,8,9
>
> I'd like to create a numeric matrix of just the numbers in this csv 
> dataset.
>
> I've tried the following program:
>
> sample.data <- read.csv("sample.csv")
> numerical.data <- as.matrix(sample.data[-1,-1])
>
> However, print(numerical.data) returns what appears to be a matrix 
> of
> characters:
>
>  x   y   z
> 2 "1" "2" "3"
> 3 "4" "5" "6"
> 4 "7" "8" "9"
>
> How do I force it to be numbers rather than characters?
>
> Thanks,
> Andrew
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at stat.math.ethz.ch 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.
> 

Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm