[R] data$ID -> I always get a NULL

[David Winsemius]

On Apr 20, 2009, at 4:33 AM, Grześ wrote:

>
> This is my result:
>
>> class(data)
> [1] "data.frame"
>
>> str(data)
> 'data.frame':	2193 obs. of  83 variables:
> $ X.ID.                               : Factor w/ 2193 levels  
> "'18201'",..:
> 1 2 3 4 5 6 7 8 9 10 ...
> $ X.kod.                       : Factor w/ 20 levels  
> "'01'","'02'",..: 1 1
> 1 1 1 1 1 1 1 1 ...
> $ X.wiel.                         : int  7 7 7 7 7 7 7 8 8 8 ...
> $ X.piech.                     : num  1 99.9 4 0.5 4 2 99.9 2 2  
> 99.9 ...
> $ X.rodz.                       : int  NA 2 4 NA 4 2 2 3 2 NA ...
>
> David Winsemius wrote:
>>
>>
>> On Apr 19, 2009, at 6:45 PM, Grześ wrote:
>>
>>>
>>> I have database write as .csv file.
>>
>> The external sorage format is not likely to be relevant. What might  
>> be
>> informative would be to produce the code that reads this file.
>>>
>>> When I want to get sth from my database I get NULL, but I know that
>>> there is
>>> sth!
>>> For example:
>>>
>>>> data$ID
>>> NULL
>>>> data$kod
>>> NULL

So the names of your columns are not "ID" and "kod" but rather "X.ID."  
and "X.kod."

Try instead:
  data$X.ID.
#and:
  data$X.kkod.     # you will need to use both the periods if your  
column names end in periods.


>>>
>>> but command like below is always recognize by R
>>>> data[2,3]
>>> [1] '082'


That must have been a different version of data, since data[2,3] from  
the dataframe above should have been   the number 7  number rather  
than a string. I would also suggest that you start naming your  
data.frames something other than "data", since that is a reserved word  
used by quite a few functions.


>>>
>>
>> Tell is what happens when you enter:
>>
>> str(data)
>> class(data)
>>
>> Perhaps the third column is not named "ID" or "kod" or the object is
>> not a data.frame, but is rather a matrix.
>>
>> -- 
>> David Winsemius
>>>
>>>
>>> In my opinion this problem is also connect with my attempt to create
>>> a tree.
>>> I always get errors.
>>>
>>>> t.tree0=rpart(ID~.,t.train)
>>> Error in eval(expr, envir, enclos) : object "ID" not found
>>>
>>>> t.tree0=rpart(kod~.,t.train)
>>> Error in eval(expr, envir, enclos) : object "kod" not found
>>>
>>> What I should do to create my simple trees?
>>>

>>> -- 

David Winsemius, MD
Heritage Laboratories
West Hartford, CT