[R] Converting dataframe to matrix

[@vi@e@gross m@iii@g oii gm@ii@com]

Daniel,

Do an experiment and see what happens, works lots of time.

I note your question may be what happens if you use factors, as in
categorical data. Factors have two sides with one being a numerical index of
sorts and the other one being a character string. 


If I make two vectors for illustration:

greek <- factor(c("alpha", "beta", "gamma"))
hebrew <- factor(c("aleph", "bet", "gimmel"))

You can see the two sides in various ways like this:

> greek
[1] alpha beta  gamma
Levels: alpha beta gamma
> as.integer(greek)
[1] 1 2 3
> as.integer(hebrew)
[1] 1 2 3


No make a data,frame like so:

mydf <- data.frame(Greek=greek, Hebrew=hebrew)

> mydf
  Greek Hebrew
1 alpha  aleph
2  beta    bet
3 gamma gimmel

Note the numbers are not visible, just text.

So converting it to a matrix will show the text/characters:

> as.matrix(mydf)
     Greek   Hebrew  
[1,] "alpha" "aleph" 
[2,] "beta"  "bet"   
[3,] "gamma" "gimmel"

If any columns happened to be numeric, a number like 666 becomes a string
like "666".

If you want the factors as integers, for some unknown reason, you might want
to make another data.frame from mydf like so:

mydf.int <- data.frame(Greek=as.integer(greek), Hebrew=as.integer(hebrew))

> mydf.int
  Greek Hebrew
1     1      1
2     2      2
3     3      3
> as.matrix(mydf.int)
     Greek Hebrew
[1,]     1      1
[2,]     2      2
[3,]     3      3
> typeof(as.matrix(mydf.int))
[1] "integer"

As others are saying, you can use as.integer safely enough as long as you
first guarantee everything is of a compatible type (such as numeric) so
result is uniform.

Or, are we missing something about your real question? Matrices are not
always a great choice and data.frames can do many of the same things for a
2-D object especially if you use some packages that ...

-----Original Message-----
From: R-help <r-help-bounces using r-project.org> On Behalf Of Daniel Lobo
Sent: Wednesday, June 25, 2025 8:24 PM
To: Rolf Turner <rolfturner using posteo.net>
Cc: r-help using r-project.org
Subject: Re: [R] Converting dataframe to matrix

My data frame looks like below

dat = structure(list(a = c(66, 100, 100, 100, 100, 100, 100, 66, 100,

66), b = c(100, 50, 100, 100, 100, 100, 100, 100, 100, 100),

    c = c(75, 25, 75, 50, 50, 50, 50, 50, 75, 25)), class =
"data.frame", row.names = c(NA,

-10L))

The values are basically categories for each column, however there may
be missing values present, which typically represented as NA.

My question is can I directly use as.matrix(na.omit(dat)) to convert
this to matrix?


On Thu, 26 Jun 2025 at 05:27, Rolf Turner <rolfturner using posteo.net> wrote:
>
>
> On Thu, 26 Jun 2025 03:45:50 +0530
> Daniel Lobo <danielobo9976 using gmail.com> wrote:
>
> > Hi,
> >
> > I have a dataframe for which all columns are numeric but categorical.
>
> I don't understand what that means.  Perhaps an example?
>
> > There are some missing values as well
> >
> > Typically, I have CSV file saved in drive, and then read it using
> > read.csv command
>
> Is that relevant?
>
> > Can I use as.matrix(na.omit(<<my dataframe loaded using read.csv>>))
> > to convert such dataframe to matrix?
> >
> > I there any data loss or change that may occur if I use as.matrix
> > command?
>
> I think your question is too vague for anyone to be able to answer this.
>
> > I remember that some experts recommends not to use as.matrix()
> > command to convert a dataframe to matrix.
>
> My guess is that the problem is that as.matrix() will coerce all of the
> columns of a data frame to a common class, which might yield unexpected
> results.
>
> > Any guidance will be very helpful.
>
> It's possible that data.matrix() might be useful.
>
> But basically you should think carefully about what the nature of the
> entries of your data frame could possibly be, and then design your code
> to accommodate all of these possibilities, throwing an error if any
> entry does not conform to any of the possibilities that you envisage.
>
> cheers,
>
> Rolf Turner
>
> --
> Honorary Research Fellow
> Department of Statistics
> University of Auckland
> Stats. Dep't. (secretaries) phone:
>          +64-9-373-7599 ext. 89622
> Home phone: +64-9-480-4619
>
> ______________________________________________
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