[R] Howto crosstable-ing......

[v.demartino2@virgilio.it]

I receive the following meteo dataset regularly, containing the average
daily temperatures (tMedia) of a certain month for 24 selected meteo-stations
(COD_WMO) whose human-readable names are in (NOME).

str(tabella)
`data.frame':	1038 obs. of  4 variables:
 $ COD_WMO: int  16045 16045 16045 16045 16045 16045 16045 16045 16045 16045
...
 $ NOME   : Factor w/ 24 levels "ALGHERO","BARI/PALESE MACCHIE",..: 22 22
22 22 22 22 22 22 22 22 ...
 $ DATE   :'POSIXct', format: chr  "2005-05-01" "2005-05-02" "2005-05-03"
"2005-05-04" ...
 $ tMedia : num  11.7 18.6 16.9 19.7 15.0 ...


Here you are a short list of it:
    COD_WMO      NOME       DATE   tMedia
505   16191 FALCONARA 2005-06-01  20.95
506   16191 FALCONARA 2005-06-02  20.15
507   16191 FALCONARA 2005-06-03  18.60
506   16191 FALCONARA 2005-06-02  20.15
507   16191 FALCONARA 2005-06-03  18.60
508   16191 FALCONARA 2005-06-04  22.30
509   16191 FALCONARA 2005-06-05     NA
510   16191 FALCONARA 2005-06-06     NA
511   16191 FALCONARA 2005-06-07  18.20
549   16206 GROSSETO 2005-06-01  20.65
550   16206 GROSSETO 2005-06-02  21.95
551   16206 GROSSETO 2005-06-03  22.25
552   16206 GROSSETO 2005-06-04  20.15
553   16206 GROSSETO 2005-06-05     NA
554   16206 GROSSETO 2005-06-06     NA
555   16206 GROSSETO 2005-06-07  22.35
.....................................................................
.....................................................................


I need to rearrange tMedia into a new dataframe whose column names are COD_WMO
 (or   NOME) and the row is DATE.

ex.
DATE            ALGHERO   BARI/PALESE ....  FALCONARA  GROSSETO ..........
2005-06-01       16.3             12.8                   17.3          
 14.0       ...........
2005-06-02       18.2               8.9                    18.0        
  17.9       ..........
...............................................................................................


I read some pieces of R-docs in the internet and run the MASS chapter 2
examples but without finding anything suitable to my purpose.

Could you please help me?

Ciao

Vittorio