R help - Jun 2015 - Formatting YYYY-MM after reading text file [RESOLVED]

I would have just assigned them all to the first day of the month, using
  as.Date( paste0(allchem$sampdate,'-01') )
(or maybe the middle of the month represented by the 15th)
and then had a variable that was of the Date class in the base R (with
which I am familiar, no small consideration).


Depending on what needs to be done with them -- plotting with a date axis?
-- calculating elapsed time between sampling events? -- I suppose one or
the other of 'yearmon' or 'Date' might be more convenient.

-Don

-- 
Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062





On 6/26/15, 12:04 PM, "R-help on behalf of Rich Shepard"
<r-help-bounces at r-project.org on behalf of rshepard at appl-ecosys.com>
wrote:
>On Fri, 26 Jun 2015, Rich Shepard wrote:
>
>> allchem$sampdate <- as.yearmon(format(%Y-%m))allchem$sampdate
>
>   Reading the yearmon help page again led me to try
> 	allchem$sampdate <- as.yearmon(allchem$sampdate)
>which produces the following structure:
>
>'data.frame':	2226 obs. of  4 variables:
>  $ stream  : chr  "B" "B" "B" "B"
...
>  $ sampdate:Class 'yearmon'  num [1:2226] 1992 1992 1992 1992 1992
...
>  $ param   : chr  "Cl" "SO4" "pH"
"Cl" ...
>  $ quant   : num  4 33 8.43 4 32 8.46 4 31 8.43 6 ...
>
>which appears to do what's needed:
>
>allchem
>      stream sampdate param    quant
>1         B Mar 1992    Cl    4.000
>2         B Mar 1992   SO4   33.000
>3         B Mar 1992    pH    8.430
>4         B Apr 1992    Cl    4.000
>5         B Apr 1992   SO4   32.000
>6         B Apr 1992    pH    8.460
>7         B May 1992    Cl    4.000
>8         B May 1992   SO4   31.000
>9         B May 1992    pH    8.430
>10        B Jun 1992    Cl    6.000
>
>   Not having before worked with dates like this I'll soon see what
>happens
>as the analyses proceed.
>
>Rich
>
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On Fri, 26 Jun 2015, MacQueen, Don wrote:
> I would have just assigned them all to the first day of the month, using
>  as.Date( paste0(allchem$sampdate,'-01') )
> (or maybe the middle of the month represented by the 15th)
> and then had a variable that was of the Date class in the base R (with
> which I am familiar, no small consideration).
Don,

   The original data had the day of the month, but that's not important. I
suppose I could leave it in and still analyze and plot by month.
> Depending on what needs to be done with them -- plotting with a date axis?
> -- calculating elapsed time between sampling events? -- I suppose one or
> the other of 'yearmon' or 'Date' might be more convenient.
   Simple is better.

Thanks,

Rich

On Jun 26, 2015, at 3:02 PM, Rich Shepard wrote:
> On Fri, 26 Jun 2015, MacQueen, Don wrote:
> 
>> I would have just assigned them all to the first day of the month,
using
>> as.Date( paste0(allchem$sampdate,'-01') )
>> (or maybe the middle of the month represented by the 15th)
>> and then had a variable that was of the Date class in the base R (with
>> which I am familiar, no small consideration).
> 
> Don,
> 
>  The original data had the day of the month, but that's not important.
I
> suppose I could leave it in and still analyze and plot by month.
I suppose I'm jumping into the middle of a conversation but I'd say
it's going to be safe to leave as a Date and then use `format(dt.val ,
"%Y-%m")` or similar for grouping and axis labels.

My 2 cents.
> 
>> Depending on what needs to be done with them -- plotting with a date
axis?
>> -- calculating elapsed time between sampling events? -- I suppose one
or
>> the other of 'yearmon' or 'Date' might be more
convenient.
> 
>  Simple is better.
Much as I appreciate the value of the yearmon-class, it's not as full
featured as class-Date.

-- 

David Winsemius
Alameda, CA, USA