[R] avoiding too many loops - reshaping data

[Dimitri Liakhovitski]

In reshape2 this does the job:

dcast(mydf,city~brand,sum)


On Wed, Nov 3, 2010 at 4:37 PM, Dimitri Liakhovitski
<dimitri.liakhovitski at gmail.com> wrote:
> Thanks a lot!
>
> Yes - I just found the reshape package too - and guess what, my math was wrong!
> reshape2 seems like the more up-to-date version of reshape.
>
> Wonder what's faster - xtabs or dcast...
> Dimitri
>
> On Wed, Nov 3, 2010 at 4:32 PM, Henrique Dallazuanna <wwwhsd at gmail.com> wrote:
>> Try this:
>>
>>  xtabs(value ~ city + brand, mydf)
>>
>> On Wed, Nov 3, 2010 at 6:23 PM, Dimitri Liakhovitski
>> <dimitri.liakhovitski at gmail.com> wrote:
>>>
>>> Hello!
>>>
>>> I have a data frame like this one:
>>>
>>>
>>> mydf<-data.frame(city=c("a","a","a","a","a","a","a","a","b","b","b","b","b","b","b","b"),
>>>  brand=c("x","x","y","y","z","z","z","z","x","x","x","y","y","y","z","z"),
>>>  value=c(1,2,11,12,111,112,113,114,3,4,5,13,14,15,115,116))
>>> (mydf)
>>>
>>> What I need to get is a data frame like the one below - cities as
>>> rows, brands as columns, and the sums of the "value" within each
>>> city/brand combination in the body of the data frame:
>>>
>>> city x   y    z
>>> a    3   23  336
>>> b    7   42  231
>>>
>>>
>>> I have written a code that involves multiple loops and subindexing -
>>> but it's taking too long.
>>> I am sure there must be a more efficient way of doing it.
>>>
>>> Thanks a lot for your hints!
>>>
>>>
>>> --
>>> Dimitri Liakhovitski
>>> Ninah Consulting
>>> www.ninah.com
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>>
>>
>> --
>> Henrique Dallazuanna
>> Curitiba-Paraná-Brasil
>> 25° 25' 40" S 49° 16' 22" O
>>
>
>
>
> --
> Dimitri Liakhovitski
> Ninah Consulting
> www.ninah.com
>



-- 
Dimitri Liakhovitski
Ninah Consulting
www.ninah.com