R help - Jul 2005 - replace matrix values with names from a dataframe

Hi,

I am looking for a way to replace matrix values with names from a dataframe.

Let me do this by example: I have a dataframe:
>data
  city.name
1    munich
2     paris
3     tokio
4    london
5    boston

each city name corresponds to only one index number (there is only one
observation for each city). After doing some matching I end up with a matrix
that looks something like this:
> X
       [,1] [,2]
  [1,]    2    4
  [2,]    5    1
  [3,]    5    3
  [4,]   12  217
  [5,]   16   13

Here the numbers in the matrix are the index numbers from my original dataset,
each row is a matched pair (so e.g. the first row tells me that obs. number 2
(i.e. Paris) was matched to obs number 4 (i.e. London)).

Now I am looking for a quick way to transform the index numbers back to city
names, so that at the end I have a matrix that looks something like this:
> X.transformed
         [,1]     [,2]
  [1,]  paris   london
  [2,] boston   munich
  [3,] boston    tokio
  [4,]     12      217
  [5,]     16       13

etc. So instead of the index number, the matrix should contain the names that
corresponds to it. In my real data, I have many many names and replacing each
value by hand would take too long. Any help is highly appreciated.

Thank you.

Regards,
Jens

maybe something like this could be helpful

city.name <- c("munich", "paris", "tokio",
"london", "boston")
X <- cbind(c(2, 5, 5), c(4, 1, 3))
####
matrix(city.name[X], ncol = 2)


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: +32/16/336899
Fax: +32/16/337015
Web: http://www.med.kuleuven.be/biostat/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm



----- Original Message ----- 
From: <jhainm at fas.harvard.edu>
To: <r-help at stat.math.ethz.ch>
Sent: Thursday, July 28, 2005 3:52 PM
Subject: [R] replace matrix values with names from a dataframe

> Hi,
>
> I am looking for a way to replace matrix values with names from a 
> dataframe.
>
> Let me do this by example: I have a dataframe:
>
>>data
>  city.name
> 1    munich
> 2     paris
> 3     tokio
> 4    london
> 5    boston
>
> each city name corresponds to only one index number (there is only 
> one
> observation for each city). After doing some matching I end up with 
> a matrix
> that looks something like this:
>
>> X
>       [,1] [,2]
>  [1,]    2    4
>  [2,]    5    1
>  [3,]    5    3
>  [4,]   12  217
>  [5,]   16   13
>
> Here the numbers in the matrix are the index numbers from my 
> original dataset,
> each row is a matched pair (so e.g. the first row tells me that obs. 
> number 2
> (i.e. Paris) was matched to obs number 4 (i.e. London)).
>
> Now I am looking for a quick way to transform the index numbers back 
> to city
> names, so that at the end I have a matrix that looks something like 
> this:
>
>> X.transformed
>         [,1]     [,2]
>  [1,]  paris   london
>  [2,] boston   munich
>  [3,] boston    tokio
>  [4,]     12      217
>  [5,]     16       13
>
> etc. So instead of the index number, the matrix should contain the 
> names that
> corresponds to it. In my real data, I have many many names and 
> replacing each
> value by hand would take too long. Any help is highly appreciated.
>
> Thank you.
>
> Regards,
> Jens
>
> ______________________________________________
> 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
>

Does the following help:

 > set.seed(1)
 > Lvls <- factor(letters[1:4])
 > A <- array(sample(4, 6, replace=TRUE), dim=c(2,3))
 > A[] <- levels(Lvls)[A]
 > A
      [,1] [,2] [,3]
[1,] "b"  "c"  "a"
[2,] "b"  "d"  "d"
 >

	  If not, PLEASE do read the posting guide! 
"http://www.R-project.org/posting-guide.html" and submit another 
question (if the process of working the posting guide does not itself 
provide enlightenment).

	  spencer graves

jhainm at fas.harvard.edu wrote:
> Hi,
> 
> I am looking for a way to replace matrix values with names from a
dataframe.
> 
> Let me do this by example: I have a dataframe:
> 
> 
>>data
> 
>   city.name
> 1    munich
> 2     paris
> 3     tokio
> 4    london
> 5    boston
> 
> each city name corresponds to only one index number (there is only one
> observation for each city). After doing some matching I end up with a
matrix
> that looks something like this:
> 
> 
>>X
> 
>        [,1] [,2]
>   [1,]    2    4
>   [2,]    5    1
>   [3,]    5    3
>   [4,]   12  217
>   [5,]   16   13
> 
> Here the numbers in the matrix are the index numbers from my original
dataset,
> each row is a matched pair (so e.g. the first row tells me that obs. number
2
> (i.e. Paris) was matched to obs number 4 (i.e. London)).
> 
> Now I am looking for a quick way to transform the index numbers back to
city
> names, so that at the end I have a matrix that looks something like this:
> 
> 
>>X.transformed
> 
>          [,1]     [,2]
>   [1,]  paris   london
>   [2,] boston   munich
>   [3,] boston    tokio
>   [4,]     12      217
>   [5,]     16       13
> 
> etc. So instead of the index number, the matrix should contain the names
that
> corresponds to it. In my real data, I have many many names and replacing
each
> value by hand would take too long. Any help is highly appreciated.
> 
> Thank you.
> 
> Regards,
> Jens
> 
> ______________________________________________
> 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
-- 
Spencer Graves, PhD
Senior Development Engineer
PDF Solutions, Inc.
333 West San Carlos Street Suite 700
San Jose, CA 95110, USA

spencer.graves at pdf.com
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