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Meenu Sahi

2009-Aug-04 18:12 UTC

[R] Caculate first difference from a dataframe; write a simulation

Dear R Users

I'm writing my first simulation in R.
I've put across my problems with a smaller example in the attachment along
with the questions.

Please help.

Best regards
Meenu
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mydat<-read.table(textConnection("Level spread change State
4.57 1.6 BlF NA
4.45 2.04 BrS NA
3.07 2.49 BlS NA
3.26 -0.26 BlF NA
2.80 0.22 BrF NA
3.22 2.5 BrS NA
4.2 -0.34 BlF NA
3.80 0.35 BrS NA
4.28 1.78 BrF NA
5.4 -0.34 BrF NA
4.89 0.24 BlF NA"), header=TRUE,as.is=TRUE)

mydat3<-data.frame(mydat)

q<-quantile(mydat3[[1]],c(0,0.25,0.75,1))
z.level<-cut(mydat3[[1]],q,include.lowest=T)
summary(z.level)

q<-quantile(mydat3[[2]],c(0,0.25,0.75,1))
z.shape<-cut(mydat3[[2]],q,include.lowest=T)
summary(z.shape)

#to identify States in mydat3
attach(mydat3)
state1<-data.frame(mydat3[spread>=-Inf & spread<= -0.02 &
Level>=-Inf & Level<=3.24,])
state2<-data.frame(mydat3[spread>-0.02 & spread<= 1.91 &
Level>=-Inf & Level<=3.24,])
state3<-data.frame(mydat3[spread>1.91 & spread<= Inf &
Level>=-Inf & Level<=3.24,])
state4<-data.frame(mydat3[spread>=-Inf & spread<= -0.02 &
Level>3.24 & Level<=4.51,])
state5<-data.frame(mydat3[spread>-0.02 & spread<= 1.91 &
Level>3.24 & Level<=4.51,])
state6<-data.frame(mydat3[spread>1.91 & spread<= Inf &
Level>3.24 & Level<=4.51,])
state7<-data.frame(mydat3[spread>=-Inf & spread<= -0.02 &
Level>4.51 & Level<=Inf,])
state8<-data.frame(mydat3[spread>-0.02 & spread<= 1.91 &
Level>4.51 & Level<=Inf,])
state9<-data.frame(mydat3[spread>1.91 & spread<= Inf &
Level>4.51 & Level<=Inf,])
detach(mydat3) 


state2<-transform(state2,
State="State2"
)
state3<-transform(state3,
State="State3"
)
state4<-transform(state5,
State="State4"
)
state5<-transform(state5,
State="State5"
)
state6<-transform(state6,
State="State6"
)
state7<-transform(state7,
State="State7"
)
state8<-transform(state8,
State="State8"
)


mydat4<-data.frame(rbind(state2,state3,state4,state5,state6,state7,state8))
## To identify states - can it be done in an easier way?
#################################################################################
##Question1:I want to calculate the first difference of mydat4[,1:2]
t<-diff(mydat4[,1:2],1)
#The command fails, why? Because it fails I've written a code for
calculating the first diff

c<-dim(mydat4)
e<-mydat4[-c[1],]
dim(e)
f<-mydat4[-1,]
dim(f)
#f
firstDiff<-data.frame(f[,-c(3:4)]-e[,-c(3:4)])

# Draw a random sample for the first differences
d<-dim(mydat3)
z<-mydat3[d[1],1:2]
z.t<-t(z)
x<-data.frame(t(firstDiff[,1:2]))
y<-sample(x[,1:2],1,replace=T)
ad<-z.t+y
##Output of ad is given below
ad
         X6
Level  5.04
spread 0.25
###################################################################################
##Question2: How can I easily identify which out of the 9 states does ad fall
into with Level =5.04 and spread=0.25?
##OUTPUT
ad
         X6
Level  5.04
spread 0.25
state  state8

##################################################################################
##Question3: I want to write a simulation of the order given below: HOw can I in
R store each
simulation result in deltay[s,t] where s keeps track of scenarios and t keeps
track of time within a scenario
Do I need to declare 
See below in 'program-language'.

For (s in 1:10000){
	yield[s,1]=z.t 
	#How can I write yield[s,]<-z.t ?
	For (t in 1:60){
		deltay[s,t] = sample(x[,1:2],1,replace=T)
		yield[s,t+1]=y[s,t]+ deltay[s,t]
	}
	write scenario s
# how can I write scenario s into a dataframe that can be stored for future
calculations
}

Gavin Simpson

2009-Aug-05 10:57 UTC

head link

[R] Caculate first difference from a dataframe; write a simulation

On Tue, 2009-08-04 at 23:42 +0530, Meenu Sahi wrote:> Dear R Users
> 
> I'm writing my first simulation in R.
> I've put across my problems with a smaller example in the attachment
along
> with the questions.
Q1 - mydat4[, 1:2] is not a matrix! It is a data.frame.
> class(mydat4[, 1:2])
[1] "data.frame"> is.matrix(mydat4[, 1:2])[1] FALSE

?diff is explicit about 'x' needing to be a numeric vector or a matrix.

Cast mydat4[, 1:2] as a matrix and it will work:
> diff(as.matrix(mydat4[,1:2]),1)   Level spread
3   0.27   2.27
6   0.15   0.01
8   0.58  -2.15
9   0.48   1.43
81 -0.48  -1.43
91  0.48   1.43
2   0.17   0.26
10  0.95  -2.38
1  -0.83   1.94
11  0.32  -1.36

HTH

G
> 
> Please help.
> 
> Best regards
> Meenu
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.-- 
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 Dr. Gavin Simpson             [t] +44 (0)20 7679 0522
 ECRC, UCL Geography,          [f] +44 (0)20 7679 0565
 Pearson Building,             [e] gavin.simpsonATNOSPAMucl.ac.uk
 Gower Street, London          [w] http://www.ucl.ac.uk/~ucfagls/
 UK. WC1E 6BT.                 [w] http://www.freshwaters.org.uk
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David Winsemius

2009-Aug-05 13:06 UTC

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[R] Caculate first difference from a dataframe; write a simulation

On Aug 4, 2009, at 2:12 PM, Meenu Sahi wrote:
> Dear R Users
>
> I'm writing my first simulation in R.
> I've put across my problems with a smaller example in the attachment  
> along
> with the questions.
>
> Please help.
See Simpson reply to Q1

##Question2: How can I easily identify which out of the 9 states does  
ad fall into with Level =5.04 and spread=0.25?
##OUTPUT
ad
          X6
Level  5.04
spread 0.25
state  state8

But spread for state7 was -0.34?????

Had it been 0.24, then this should work (some of the time.)
 > subset(mydat4, Level == 5.4 & spread==0.25)
[1] Level  spread change State
<0 rows> (or 0-length row.names)

Perhaps you meant to specify an "or" condition?

 > subset(mydat4, Level == 5.4 | spread==0.24)
    Level spread change  State
10  5.40  -0.34    BrF State7
11  4.89   0.24    BlF State8

>
> Best regards
> Meenu
> <Example.txt>______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
Heritage Laboratories
West Hartford, CT

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