Re: [R] replace matrix values with names from a dataframe

From: Spencer Graves <spencer.graves_at_pdf.com>
Date: Sat 30 Jul 2005 - 02:03:27 EST

          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@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
>
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-- 
Spencer Graves, PhD
Senior Development Engineer
PDF Solutions, Inc.
333 West San Carlos Street Suite 700
San Jose, CA 95110, USA

spencer.graves@pdf.com
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Received on Sat Jul 30 02:18:14 2005

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