[R] as.Date from data.frame

[Steve Lianoglou]

Hi,

On Nov 11, 2009, at 1:06 PM, separent wrote:

>
> #Hello,
>
> #I loaded data using read.table - I needed to convert a row in the  
> data
> frame to date class:
>
>> data
>
> V1          V2          V3          V4
> 1  2008-05-19  2008-04-19  2008-03-21  2008-02-22
> 2 38.16999817 30.70999908 36.86000061 35.18999863
> 3 37.47999954 29.95000076 36.45999908 35.36000061
> 4 37.47999954 30.14999962 36.47000122 35.36000061
> 5 37.84999847 30.56999969 36.84000015 35.74000168
> 6 38.38999939 31.14999962 37.34000015 36.27000046
> 7 39.11000061 31.90999985 38.02999878 36.97999954
> 8 39.81000137 32.65000153 38.68000031 37.63999939
> 9 40.47000122 33.34999847 39.27999878 38.27000046
>
>> data[1,]
>          V1         V2         V3         V4
> 1 2008-05-19 2008-04-19 2008-03-21 2008-02-22
>
>> dates1<-as.Date(data[1,])

I think this should work if data[1,] returns a vector of characters:

R> d <- c("2008-05-19", "2008-05-30")
R> dd <- as.Date(d)
R> is(dd)
[1] "Date"     "oldClass"

Is your first row being treated as factors? Maybe if you convert to  
character first it should work?

R> dates1<-as.Date(as.character(data[1,]))

But the fact that it works for as.Date(data[1,1]) make it a bit  
weird ...

-steve

> do not know how to convert 'dates[1,]' to class "Date"
>
> # However, I can individually convert them all:
>
>> dates1.1<-as.Date(data[1,1])
>
>> dates1.1
> [1] "2008-05-19"
>
> # How can I change the class of the date over the entire row (my  
> original
> file contains more than one hundred rows)?
> # Thank you very much.
> -- 
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>
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--
Steve Lianoglou
Graduate Student: Computational Systems Biology
   |  Memorial Sloan-Kettering Cancer Center
   |  Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact