[R] replace matrix values with names from a dataframe

[Dimitris Rizopoulos]

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
>
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