[R] Changing date format

[Göran Broström]

On 2014-10-07 11:27, Jim Lemon wrote:
> On Tue, 7 Oct 2014 10:32:42 AM Frederic Ntirenganya wrote:
>> Dear All,
>>
>> How can I change the format of date of day of the year ? for
> example r
>> (i.e. "17 Apr" rather than "108").
>>
>> The following is the type of the dataset I have
>>
>> head(Samaru)
>>    Year Start End Length
>> 1 1930   108 288    180
>> 2 1931   118 288    170
>> 3 1932   115 295    180
>> 4 1933   156 294    138
>> 5 1934   116 291    175
>> 6 1935   134 288    154
>>
> Hi Frederic,
> The easiest method I can think of is this:
>
> Samaru$Start<-format(as.Date(
>   paste(Samaru$Year,"01-01",sep="-"))+Samaru$Start,
>   "%b %d")
> Samaru$End<-format(as.Date(
>   paste(Samaru$Year,"01-01",sep="-"))+Samaru$End,
>   "%b %d")

In the package 'eha' I have a function 'toDate':

 > require(eha)
 > toDate(1930 + 108/365)
[1] "1930-04-19"

(Interestingly, we are all wrong; the correct answer seems to be 
"1930-04-18")

 > toDate
function (times)
{
     if (!is.numeric(times))
         stop("Argument must be numeric")
     times * 365.2425 + as.Date("0000-01-01")
}

The 'inverse' function is 'toTime'.

Sometimes it misses by one day; not very important in my applications, 
but may be otherwise.

Göran B.

> Samaru
>
>    Year  Start    End Length
> 1 1930 Apr 19 Oct 16    180
> 2 1931 Apr 29 Oct 16    170
> 3 1932 Apr 25 Oct 22    180
> 4 1933 Jun 06 Oct 22    138
> 5 1934 Apr 27 Oct 19    175
> 6 1935 May 15 Oct 16    154
>
> Jim
>
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