[R] daily maximum temperature

[David Winsemius]

On Nov 23, 2012, at 10:04 AM, Dominic Roye wrote:

> Hello,
>
> I want to filter the daily maximum temperature. For this i made this
> skript, but it come out wrong results. Can anybody help me?
>
> Thanks for your help!
>
> Best regards
>
>
> datos$X <- as.POSIXct(strptime(datos$X, "%d/%m/%Y %H:%M:%S"))
> z <- aggregate(zoo(datos$Ta), as.POSIXct(datos$X), max)
>
You do not say what you mean by "filter the daily maximum temperature"  
but perhaps you just want the maimums on a given date? Perhaps:

z <- aggregate(zoo(datos$Ta), as.Date(as.character(datos$X)), max,  
na.rm=TRUE)

# You won't be calculating by "date" unless you do some sort of  
conversion. I see below that you have X as a factor so it might be  
needed to calculate using as.character for a factor.)

(Not sure that the zoo(.) is needed, and I'm a bit worried that it is  
there. You seem to have convinced as.POSIXct to use 2010-01-01 as the  
strating data which seems weird)

-- 
David.


>
>> str(datos)
> 'data.frame':   17137 obs. of  5 variables:
> $ X : Factor w/ 17136 levels "00/01/1900 0:00:00",..: 2 3 4 5 6 7 8  
> 9 10 11 ...
> $ Ta: num  5.28 5.45 5.54 5.54 5.51 5.51 5.5 5.56 5.58 5.63 ...
> $ HR: int  100 100 100 100 100 100 100 100 100 100 ...
> $ RS: int  0 0 0 0 0 0 0 0 0 0 ...
> $ v : num  2.3 2.5 1.1 2.3 2.2 2.1 2.2 2.9 2.4 2.6 ...
>
>
>
> str(z)
> ‘zoo’ series from 2010-01-01 00:10:00 to 2010-04-29 23:50:00
>  Data: num [1:17129] 5.28 5.45 5.54 5.54 5.51 5.51 5.5 5.56 5.58  
> 5.63 ...
>  Index:  POSIXct[1:17129], format: "2010-01-01 00:10:00" "2010-01-01
> 00:20:00" "2010-01-01 00:30:00" "2010-01-01 00:40:00" ...
>>
>
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David Winsemius, MD
Alameda, CA, USA