[R] How to copy data from data.frame to matrix

[Uwe Ligges]

On 04.03.2011 11:38, Dmitrij Kudriavcev wrote:
> Hello
>
> Let's say, my data.frame is
>
> symbol,day,value
> A, 2010-01-01, 0.8888
> A, 2010-01-02, 0.6666
> B, 2010-01-01, 0.7777
>
> i need to get matrix as


See ?reshape, in this case if you data.frame is in dat:

reshape(dat, v.names="value", direction="wide",
         idvar="day", timevar="symbol")

Uwe Ligges



> , A, B
> 2010-01-01, 0.8888, 0.7777
> 2010-01-02, 0.6666, NA
>
> where A and B is columns name and date used as row name
>
> I found a way how to do it with tapply function, is it a best way (i will
> need to do this pretty offen and wish to save some time)
>
> Cheers,
> Dima
>
>
> 2011/3/4 Ivan Calandra<ivan.calandra at uni-hamburg.de>
>
>> Hi,
>>
>> Let's say your data.frame is called df:
>> df<- data.frame(a=rnorm(10), b=rnorm(10))
>> data.matrix<- as.matrix(df)
>>
>> This should work, but be careful with coercion if you have different modes
>> in your data.frame
>>
>> HTH,
>> Ivan
>>
>> PS: next time, provide a reproducible example, using dput() for example
>>
>> Le 3/4/2011 07:08, Dmitrij Kudriavcev a écrit :
>>
>>> Hello
>>>
>>> I'm a new in R
>>> I have a large data.frame "s" (this is actualy just a table in mysql) :
>>>
>>>   names(s)
>>>>
>>> [1] "symbols", "day", "value"
>>>
>>> I need to convert it to simple matrix. I have define this matrix like
>>> this:
>>>
>>>   data.matrix<- matrix(nrow=nDays, ncol=nSymbols, dimnames=list(days,
>>>>
>>> symbols))
>>>
>>> then i just copy values to the matrix using for() loop, but it seems to
>>> take
>>> very long time. Is is a more fast way to do it in R? I know, what i can
>>> just
>>> gyve s$value as source data to the matrix, but problem is, what for some
>>> symbols couple days could be just missed.
>>>
>>> Cheers,
>>> Dima
>>>
>>>         [[alternative HTML version deleted]]
>>>
>>> ______________________________________________
>>> 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.
>>>
>>>
>> --
>> Ivan CALANDRA
>> PhD Student
>> University of Hamburg
>> Biozentrum Grindel und Zoologisches Museum
>> Abt. Säugetiere
>> Martin-Luther-King-Platz 3
>> D-20146 Hamburg, GERMANY
>> +49(0)40 42838 6231
>> ivan.calandra at uni-hamburg.de
>>
>> **********
>> http://www.for771.uni-bonn.de
>> http://webapp5.rrz.uni-hamburg.de/mammals/eng/1525_8_1.php
>>
>>
>> ______________________________________________
>> 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.
>>
>
> 	[[alternative HTML version deleted]]
>
>
>
>
> ______________________________________________
> 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.