[R] replace matrix values with names from a dataframe

[jhainm@fas.harvard.edu]

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