[R] Converting a data frame to matrix

[Petr PIKAL]

Hi

r-help-bounces at r-project.org napsal dne 28.03.2008 10:18:20:

> Adrian Johnson wrote:
> > Hello:
> > 
> > I have a tab delim file with 100 rows and 100 columns.
> > 
> > I have numerical values in this table. What I want is to create an 
image

Probably not. See below.

> > color map with color gradation.
> > 
> > my values range from -5 to 0. max value is 0.
> > 
> > to acheive this, I need to convert my data.frame into matrix.
> > 
> > I tried following :
> > 
> > mydf <- read.table('mytable',sep='\t',header=T)
> > mydf1 <- mydf[,2:100]
> > colnames(mydf1) <- as.character(mydf[,1])

It should be probably 

rownames(mydf1) <- as.character(mydf[,1])

mydf<-rnorm(100*100)
mydf<-matrix(mydf, 100,100)
mydf<-data.frame(mydf)
mydf1<-mydf[,2:100]
colnames(mydf1)<-as.character(mydf[,1])
Error in names(x) <- value : 
  'names' attribute [100] must be the same length as the vector [99]
 


> > 
> > here comes the trouble:
> > 
> > mymat <- as.matrix(mydf1)
> > 
> > -- numerical values become character values.  -1 becomes "-1"

If you had all values in data frame really numeric it shall stay as 
numeric also in your matrix. Try

str(mydf1)

and you will probably find out that some variables are factors/character. 
Therefore as.matrix transfers **all** values to character as matrix can 
not mix data of various type.



> > 
> > mymat <- data.matrix(mydf1)
> > 
> > -- whole matrix is filled with 1,2 and 3.
> > 
> > Is there any other way I can do this.
> > 
> > say row names are city schools
> > colnames  are student names
> > 
> Hi Adrian,
> Have you looked at color2d.matplot in the plotrix package?
> 
> Jim
> 
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