[R] Function on columns of a dataframe

[David Winsemius]

On Jul 9, 2010, at 9:46 AM, Eik Vettorazzi wrote:

> Hi Nils,
> have a look at
> ?tapply
> hth.

Perhaps this will be part way there (I couldn't really figure out the  
desired structure of the final object):
 > lapply( bla[, -(1:2)], function(x) tapply(x, bla$cat, max) )
$v1
      cat1      cat2      cat3      cat4      cat5      cat6
0.4634519 0.4062700 0.4816403 0.6354560 0.6663811 0.5260832

$v2
      cat1      cat2      cat3      cat4      cat5      cat6
0.5274645 0.4282639 0.4996033 0.3558259 0.2154201 0.3934063

$v3
      cat1      cat2      cat3      cat4      cat5      cat6
0.6051479 0.4443707 0.3538144 0.3646292 0.5059900 0.3545962

$v4
      cat1      cat2      cat3      cat4      cat5      cat6
0.7586322 0.8419526 0.9456385 0.1907295 0.7573575 0.6412563


>
> Am 09.07.2010 15:37, schrieb LogLord:
>> Hi,
>>
>> I would like to assign the largest value of a column to a specific  
>> category
>> and repeat this for each column (v1 - v4).
>>
>>
>>> x=c(1:12)
>>> cat 
>>> = 
>>> c 
>>> ("cat1 
>>> ","cat5 
>>> ","cat2 
>>> ","cat2","cat1","cat5","cat3","cat4","cat5","cat2","cat3","cat6")
>>> v1=rnorm(12,0.5,0.1)
>>> v2=rnorm(12,0.3,0.2)
>>> v3=rnorm(12,0.4,0.1)
>>> v4=rnorm(12,0.6,0.3)
>>> bla=data.frame(x,cat,v1,v2,v3,v4)
>>> bla
>>>
>>    x  cat        v1         v2        v3         v4
>> 1   1 cat1 0.4013144 0.54839317 0.3946393  0.8679266
>> 2   2 cat5 0.4595873 0.45788906 0.4030078  0.5919596
>> 3   3 cat2 0.4542865 0.21516928 0.2777649  0.6112099
>> 4   4 cat2 0.4787950 0.06252512 0.5095611  0.6450795
>> 5   5 cat1 0.4910746 0.56591049 0.5151813  0.8465181
>> 6   6 cat5 0.4194397 0.16592579 0.4361643  0.6415192
>> 7   7 cat3 0.6148564 0.32240342 0.2690108  0.7114133
>> 8   8 cat4 0.6174652 0.28076152 0.4577064 -0.2567284
>> 9   9 cat5 0.4775395 0.28611768 0.4660210  0.4634120
>> 10 10 cat2 0.4802962 0.03715569 0.4506361  1.0063235
>> 11 11 cat3 0.6495094 0.33303172 0.3352933  1.4390324
>> 12 12 cat6 0.4891481 0.45355589 0.3880739  0.7831656
>>
>>>
>> I can assign this by the sqldf() command for each column but I  
>> would like to
>> automate this as I have many columns.
>>
>>
>>> select=sqldf("select cat, max(v1) FROM bla GROUP BY cat")
>>> select
>>>
>>   cat   max(v1)
>> 1 cat1 0.4910746
>> 2 cat2 0.4802962
>> 3 cat3 0.6495094
>> 4 cat4 0.6174652
>> 5 cat5 0.4775395
>> 6 cat6 0.4891481
>>
>>>
>> Finally, I would like to have a dataframe where where the cat is  
>> followed by
>> each column maximum.
>>
>> Thanks for your help!
>>
>
> -- 
> Eik Vettorazzi
> Institut für Medizinische Biometrie und Epidemiologie
> Universitätsklinikum Hamburg-Eppendorf
>
> Martinistr. 52
> 20246 Hamburg
>
> T ++49/40/7410-58243
> F ++49/40/7410-57790
>
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David Winsemius, MD
West Hartford, CT