[R] when to use & pros/cons of dataframe vs. matrix?

[arun]

Hi,
set.seed(24)
dat1<-data.frame(X=sample(letters,20,replace=TRUE),Y=sample(1:40,20,replace=TRUE),stringsAsFactors=FALSE)
mat1<-as.matrix(dat1)
 sapply(dat1,class)
#          X           Y 
#"character"   "integer" 

sapply(split(mat1,col(mat1)),class)
#          1           2 
#"character" "character" 
str(as.data.frame(mat1))
#'data.frame':    20 obs. of  2 variables:
# $ X: Factor w/ 14 levels "b","d","f","g",..: 5 3 11 8 10 14 5 12 13 4 ...
# $ Y: Factor w/ 14 levels "10","13","15",..: 12 5 9 13 14 8 12 6 7 4 ...

If you have data of the same type, matrix would be faster when compared to data.frame.
set.seed(245)
mat2<- matrix(sample(1:50,3*1e7,replace=TRUE),ncol=3)

dat2<- as.data.frame(mat2)
system.time(res1<- rowSums(mat2))
#   user  system elapsed 
#  0.132   0.016   0.201 
 system.time(res2<- rowSums(dat2))
#   user  system elapsed 
#  0.376   0.056   0.447 
 identical(res1,res2)
#[1] TRUE


A.K.



----- Original Message -----
From: Anika Masters <anika.masters at gmail.com>
To: R help <r-help at r-project.org>
Cc: 
Sent: Thursday, June 27, 2013 2:26 PM
Subject: [R] when to use & pros/cons of dataframe vs. matrix?

When "should" I use a dataframe vs. a matrix?  What are the pros and cons?
If I have data of all the same type, am I usually better off using a
matrix and not a dataframe?
What are the advantages if any of using a dataframe vs. a matrix?
(rownames and column names perhaps?)

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