[R] daily maximum temperature

[arun]

Hi,
Since you mentioned filtering the daily maximum temperature, this may help:
datos<-read.table(text="
X, Ta, HR, RS, v
1/1/2010 1:00:00,5.28,100,0,2.3
1/1/2010 6:00:00,5.45,100,0,2.5
1/1/2010 11:00:00,5.51,100,0,1.1
2/1/2010 1:00:00,5.33,100,0,2.1
2/1/2010 6:00:00,5.48,100,0,2.3
2/1/2010 11:00:00,5.64,100,0,2.4    
3/1/2010 1:00:00,5.12,100,0,2.0
3/1/2010 6:00:00,5.40,100,0,2.3
3/1/2010 11:00:00,5.32,100,0,1.7
",sep=",",header=TRUE,stringsAsFactors=FALSE)
library(zoo)
z<-zoo(datos[,-1],order.by=as.POSIXct(datos[,1],format="%d/%m/%Y %H:%M:%S"))

 aggregate(z$Ta,by=list(as.Date(index(z))),max) #gives the daily maximum temperatures
#2010-01-01 2010-01-02 2010-01-03 
 #     5.51       5.64       5.40 


For filtering the data:


flag<-unlist(lapply(split(z,as.Date(index(z))),function(x) data.frame(x[,1]==max(x[,1]))),use.names=F)
 z1<-transform(z,flag=flag)
z2<-z1[,1:4][z1$flag==1,] #filtered the maximum daily temp data 
z2
#                      Ta  HR RS   v
#2010-01-01 11:00:00 5.51 100  0 1.1
#2010-01-02 11:00:00 5.64 100  0 2.4
#2010-01-03 06:00:00 5.40 100  0 2.3

 str(z2)
#‘zoo’ series from 2010-01-01 11:00:00 to 2010-01-03 06:00:00
 # Data: num [1:3, 1:4] 5.51 5.64 5.4 100 100 100 0 0 0 1.1 ...
 #- attr(*, "dimnames")=List of 2
  #..$ : NULL
  #..$ : chr [1:4] "Ta" "HR" "RS" "v"
  #Index:  POSIXct[1:3], format: "2010-01-01 11:00:00" "2010-01-02 11:00:00" ...

#or
z3<-z
 z3$Max<-ave(z[,1],as.Date(index(z)),FUN=max)
 z4<-z3[,-5][z3$Ta==z3$Max,]
 z4
#                      Ta  HR RS   v
#2010-01-01 11:00:00 5.51 100  0 1.1
#2010-01-02 11:00:00 5.64 100  0 2.4
#2010-01-03 06:00:00 5.40 100  0 2.3

Hope it helps

A.K.



----- Original Message -----
From: Dominic Roye <dominic.roye at gmail.com>
To: r-help at r-project.org
Cc: 
Sent: Friday, November 23, 2012 1:04 PM
Subject: [R] daily maximum temperature

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)


> 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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